Implement tracing interface for v8

src/tracing/trace-event.h

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are

[Yang, 2015/03/13 07:52:10]

I assume that this file originates from Chromium? How do we make sure this stays
in sync?

[fmeawad, 2015/03/17 01:18:04]

It does originate from chromium. At the moment there is no guarantee that it
would stay in sync. But there are multiple instance of it in third_parties
already (e.g. Blink, Skia, Webrtc, Angle, ...). So it is known to be everywhere,
so changing it is limited.
There is a plan to make it in its own library, but not in the near future.
Even if it gets out of sink (which might happen if V8 or other library have
different needs), it will always use the same interface (as defined in
v8-tracing.h).

+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This header file defines the set of trace_event macros without specifying
+// how the events actually get collected and stored. If you need to expose trace
+// events to some other universe, you can copy-and-paste this file as well as
+// trace_event.h, modifying the macros contained there as necessary for the
+// target platform. The end result is that multiple libraries can funnel events
+// through to a shared trace event collector.
+
+// Trace events are for tracking application performance and resource usage.
+// Macros are provided to track:
+//    Begin and end of function calls
+//    Counters
+//
+// Events are issued against categories. Whereas LOG's
+// categories are statically defined, TRACE categories are created
+// implicitly with a string. For example:
+//   TRACE_EVENT_INSTANT0("MY_SUBSYSTEM", "SomeImportantEvent",
+//                        TRACE_EVENT_SCOPE_THREAD)
+//
+// It is often the case that one trace may belong in multiple categories at the
+// same time. The first argument to the trace can be a comma-separated list of
+// categories, forming a category group, like:
+//
+// TRACE_EVENT_INSTANT0("input,views", "OnMouseOver", TRACE_EVENT_SCOPE_THREAD)
+//
+// We can enable/disable tracing of OnMouseOver by enabling/disabling either
+// category.
+//
+// Events can be INSTANT, or can be pairs of BEGIN and END in the same scope:
+//   TRACE_EVENT_BEGIN0("MY_SUBSYSTEM", "SomethingCostly")
+//   doSomethingCostly()
+//   TRACE_EVENT_END0("MY_SUBSYSTEM", "SomethingCostly")
+// Note: our tools can't always determine the correct BEGIN/END pairs unless
+// these are used in the same scope. Use ASYNC_BEGIN/ASYNC_END macros if you
+// need them to be in separate scopes.
+//
+// A common use case is to trace entire function scopes. This
+// issues a trace BEGIN and END automatically:
+//   void doSomethingCostly() {
+//     TRACE_EVENT0("MY_SUBSYSTEM", "doSomethingCostly");
+//     ...
+//   }
+//
+// Additional parameters can be associated with an event:
+//   void doSomethingCostly2(int howMuch) {
+//     TRACE_EVENT1("MY_SUBSYSTEM", "doSomethingCostly",
+//         "howMuch", howMuch);
+//     ...
+//   }
+//
+// The trace system will automatically add to this information the
+// current process id, thread id, and a timestamp in microseconds.
+//
+// To trace an asynchronous procedure such as an IPC send/receive, use
+// ASYNC_BEGIN and ASYNC_END:
+//   [single threaded sender code]
+//     static int send_count = 0;
+//     ++send_count;
+//     TRACE_EVENT_ASYNC_BEGIN0("ipc", "message", send_count);
+//     Send(new MyMessage(send_count));
+//   [receive code]
+//     void OnMyMessage(send_count) {
+//       TRACE_EVENT_ASYNC_END0("ipc", "message", send_count);
+//     }
+// The third parameter is a unique ID to match ASYNC_BEGIN/ASYNC_END pairs.
+// ASYNC_BEGIN and ASYNC_END can occur on any thread of any traced process.
+// Pointers can be used for the ID parameter, and they will be mangled
+// internally so that the same pointer on two different processes will not
+// match. For example:
+//   class MyTracedClass {
+//    public:
+//     MyTracedClass() {
+//       TRACE_EVENT_ASYNC_BEGIN0("category", "MyTracedClass", this);
+//     }
+//     ~MyTracedClass() {
+//       TRACE_EVENT_ASYNC_END0("category", "MyTracedClass", this);
+//     }
+//   }
+//
+// Trace event also supports counters, which is a way to track a quantity
+// as it varies over time. Counters are created with the following macro:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter", g_myCounterValue);
+//
+// Counters are process-specific. The macro itself can be issued from any
+// thread, however.
+//
+// Sometimes, you want to track two counters at once. You can do this with two
+// counter macros:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter0", g_myCounterValue[0]);
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter1", g_myCounterValue[1]);
+// Or you can do it with a combined macro:
+//   TRACE_COUNTER2("MY_SUBSYSTEM", "myCounter",
+//       "bytesPinned", g_myCounterValue[0],
+//       "bytesAllocated", g_myCounterValue[1]);
+// This indicates to the tracing UI that these counters should be displayed
+// in a single graph, as a summed area chart.
+//
+// Since counters are in a global namespace, you may want to disambiguate with a
+// unique ID, by using the TRACE_COUNTER_ID* variations.
+//
+// By default, trace collection is compiled in, but turned off at runtime.
+// Collecting trace data is the responsibility of the embedding
+// application. In Chrome's case, navigating to about:tracing will turn on
+// tracing and display data collected across all active processes.
+//
+//
+// Memory scoping note:
+// Tracing copies the pointers, not the string content, of the strings passed
+// in for category_group, name, and arg_names.  Thus, the following code will
+// cause problems:
+//     char* str = strdup("importantName");
+//     TRACE_EVENT_INSTANT0("SUBSYSTEM", str);  // BAD!
+//     free(str);                   // Trace system now has dangling pointer
+//
+// To avoid this issue with the |name| and |arg_name| parameters, use the
+// TRACE_EVENT_COPY_XXX overloads of the macros at additional runtime overhead.
+// Notes: The category must always be in a long-lived char* (i.e. static const).
+//        The |arg_values|, when used, are always deep copied with the _COPY
+//        macros.
+//
+// When are string argument values copied:
+// const char* arg_values are only referenced by default:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", "literal string is only referenced");
+// Use TRACE_STR_COPY to force copying of a const char*:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", TRACE_STR_COPY("string will be copied"));
+// std::string arg_values are always copied:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", std::string("string will be copied"));
+//
+//
+// Thread Safety:
+// A thread safe singleton and mutex are used for thread safety. Category
+// enabled flags are used to limit the performance impact when the system
+// is not enabled.
+//
+// TRACE_EVENT macros first cache a pointer to a category. The categories are
+// statically allocated and safe at all times, even after exit. Fetching a
+// category is protected by the TraceLog::lock_. Multiple threads initializing
+// the static variable is safe, as they will be serialized by the lock and
+// multiple calls will return the same pointer to the category.
+//
+// Then the category_group_enabled flag is checked. This is a unsigned char, and
+// not intended to be multithread safe. It optimizes access to AddTraceEvent
+// which is threadsafe internally via TraceLog::lock_. The enabled flag may
+// cause some threads to incorrectly call or ip calling AddTraceEvent near
+// the time of the system being enabled or disabled. This is acceptable as
+// we tolerate some data loss while the system is being enabled/disabled and
+// because AddTraceEvent is threadsafe internally and checks the enabled state
+// again under lock.
+//
+// Without the use of these static category pointers and enabled flags all
+// trace points would carry a significant performance cost of acquiring a lock
+// and resolving the category.
+
+#ifndef SRC_TRACING_TRACE_EVENT_H_
+#define SRC_TRACING_TRACE_EVENT_H_
+
+#include "include/v8-tracing.h"
+
+// By default, const char* argument values are assumed to have long-lived scope
+// and will not be copied. Use this macro to force a const char* to be copied.
+#define TRACE_STR_COPY(str) v8::tracing_internals::TraceStringWithCopy(str)
+
+// By default, uint64 ID argument values are not mangled with the Process ID in
+// TRACE_EVENT_ASYNC macros. Use this macro to force Process ID mangling.
+#define TRACE_ID_MANGLE(id) v8::tracing_internals::TraceID::ForceMangle(id)
+
+// By default, pointers are mangled with the Process ID in TRACE_EVENT_ASYNC
+// macros. Use this macro to prevent Process ID mangling.
+#define TRACE_ID_DONT_MANGLE(id) v8::tracing_internals::TraceID::DontMangle(id)
+
+// Records a pair of begin and end events called "name" for the current
+// scope, with 0, 1 or 2 associated arguments. If the category is not
+// enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT0(category_group, name) \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name)
+#define TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, arg1_name, arg1_val)
+#define TRACE_EVENT2(category_group, name, arg1_name, arg1_val, arg2_name,   \
+                     arg2_val)                                               \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, arg1_name, arg1_val, \
+                                  arg2_name, arg2_val)
+
+// Records events like TRACE_EVENT2 but uses |memory_tag| for memory tracing.
+// Use this where |name| is too generic to accurately aggregate allocations.
+#define TRACE_EVENT_WITH_MEMORY_TAG2(category, name, memory_tag, arg1_name, \
+                                     arg1_val, arg2_name, arg2_val)         \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, arg1_name, arg1_val,      \
+                                  arg2_name, arg2_val)
+
+// UNSHIPPED_TRACE_EVENT* are like TRACE_EVENT* except that they are not
+// included in official builds.
+
+#if OFFICIAL_BUILD
+#undef TRACING_IS_OFFICIAL_BUILD
+#define TRACING_IS_OFFICIAL_BUILD 1
+#elif !defined(TRACING_IS_OFFICIAL_BUILD)
+#define TRACING_IS_OFFICIAL_BUILD 0
+#endif
+
+#if TRACING_IS_OFFICIAL_BUILD
+#define UNSHIPPED_TRACE_EVENT0(category_group, name) (void)0
+#define UNSHIPPED_TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT2(category_group, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                       \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category_group, name, scope) (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, \
+                                       arg1_val)                               \
+  (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, \
+                                       arg1_val, arg2_name, arg2_val)          \
+  (void)0
+#else
+#define UNSHIPPED_TRACE_EVENT0(category_group, name) \
+  TRACE_EVENT0(category_group, name)
+#define UNSHIPPED_TRACE_EVENT1(category_group, name, arg1_name, arg1_val) \
+  TRACE_EVENT1(category_group, name, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT2(category_group, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                       \
+  TRACE_EVENT2(category_group, name, arg1_name, arg1_val, arg2_name, arg2_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category_group, name, scope) \
+  TRACE_EVENT_INSTANT0(category_group, name, scope)
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, \
+                                       arg1_val)                               \
+  TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, \
+                                       arg1_val, arg2_name, arg2_val)          \
+  TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, arg1_val,       \
+                       arg2_name, arg2_val)
+#endif
+
+// Records a single event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_INSTANT0(category_group, name, scope)                   \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE | scope)
+#define TRACE_EVENT_INSTANT1(category_group, name, scope, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val)
+#define TRACE_EVENT_INSTANT2(category_group, name, scope, arg1_name, arg1_val, \
+                             arg2_name, arg2_val)                              \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val, \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_INSTANT0(category_group, name, scope)              \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY | scope)
+#define TRACE_EVENT_COPY_INSTANT1(category_group, name, scope, arg1_name,   \
+                                  arg1_val)                                 \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY | scope, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_INSTANT2(category_group, name, scope, arg1_name,      \
+                                  arg1_val, arg2_name, arg2_val)               \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, category_group, name,    \
+                           TRACE_EVENT_FLAG_COPY | scope, arg1_name, arg1_val, \
+                           arg2_name, arg2_val)
+
+// Sets the current sample state to the given category and name (both must be
+// constant strings). These states are intended for a sampling profiler.
+// Implementation note: we store category and name together because we don't
+// want the inconsistency/expense of storing two pointers.
+// |thread_bucket| is [0..2] and is used to statically isolate samples in one
+// thread from others.
+#define TRACE_EVENT_SET_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                  name)                    \
+  v8::tracing_internals::TraceEventSamplingStateScope<bucket_number>::Set( \
+      category "\0" name)
+
+// Returns a current sampling state of the given bucket.
+#define TRACE_EVENT_GET_SAMPLING_STATE_FOR_BUCKET(bucket_number) \
+  v8::tracing_internals::TraceEventSamplingStateScope<bucket_number>::Current()
+
+// Creates a scope of a sampling state of the given bucket.
+//
+// {  // The sampling state is set within this scope.
+//    TRACE_EVENT_SAMPLING_STATE_SCOPE_FOR_BUCKET(0, "category", "name");
+//    ...;
+// }
+#define TRACE_EVENT_SCOPED_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                     name)                    \
+  v8::tracing_internals::TraceEventSamplingStateScope<bucket_number>          \
+      traceEventSamplingScope(category "\0" name);
+
+// Syntactic sugars for the sampling tracing in the main thread.
+#define TRACE_EVENT_SCOPED_SAMPLING_STATE(category, name) \
+  TRACE_EVENT_SCOPED_SAMPLING_STATE_FOR_BUCKET(0, category, name)
+#define TRACE_EVENT_GET_SAMPLING_STATE() \
+  TRACE_EVENT_GET_SAMPLING_STATE_FOR_BUCKET(0)
+#define TRACE_EVENT_SET_SAMPLING_STATE(category, name) \
+  TRACE_EVENT_SET_SAMPLING_STATE_FOR_BUCKET(0, category, name)
+
+
+// Records a single BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_BEGIN0(category_group, name)                          \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_BEGIN1(category_group, name, arg1_name, arg1_val)     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_BEGIN2(category_group, name, arg1_name, arg1_val,     \
+                           arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val,    \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_BEGIN0(category_group, name)                     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_BEGIN1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_BEGIN2(category_group, name, arg1_name, arg1_val, \
+                                arg2_name, arg2_val)                       \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val,     \
+                           arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_BEGINx but with a custom |at| timestamp provided.
+// - |id| is used to match the _BEGIN event with the _END event.
+//   Events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+#define TRACE_EVENT_BEGIN_WITH_ID_TID_AND_TIMESTAMP0(category_group, name, id, \
+                                                     thread_id)                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id,      \
+      timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_COPY_BEGIN_WITH_ID_TID_AND_TIMESTAMP0(category_group,      \
+                                                          name, id, thread_id) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id, thread_id,      \
+      timestamp, TRACE_EVENT_FLAG_COPY)
+
+// Records a single END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_END0(category_group, name)                          \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_END1(category_group, name, arg1_name, arg1_val)     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_END2(category_group, name, arg1_name, arg1_val, arg2_name, \
+                         arg2_val)                                             \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,        \
+                           TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val,         \
+                           arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_END0(category_group, name)                     \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_END1(category_group, name, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_END2(category_group, name, arg1_name, arg1_val, \
+                              arg2_name, arg2_val)                       \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, category_group, name,  \
+                           TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val,   \
+                           arg2_name, arg2_val)
+
+// Similar to TRACE_EVENT_ENDx but with a custom |at| timestamp provided.
+// - |id| is used to match the _BEGIN event with the _END event.
+//   Events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+#define TRACE_EVENT_END_WITH_ID_TID_AND_TIMESTAMP0(category_group, name, id, \
+                                                   thread_id)                \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                        \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id,      \
+      timestamp, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_COPY_END_WITH_ID_TID_AND_TIMESTAMP0(category_group, name, \
+                                                        id, thread_id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id, thread_id,       \
+      timestamp, TRACE_EVENT_FLAG_COPY)
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER1(category_group, name, value)                         \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, "value",                  \
+                           static_cast<int>(value))
+#define TRACE_COPY_COUNTER1(category_group, name, value)                    \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY, "value",                  \
+                           static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER2(category_group, name, value1_name, value1_val,       \
+                       value2_name, value2_val)                             \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE, value1_name,              \
+                           static_cast<int>(value1_val), value2_name,       \
+                           static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER2(category_group, name, value1_name, value1_val,  \
+                            value2_name, value2_val)                        \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, category_group, name, \
+                           TRACE_EVENT_FLAG_COPY, value1_name,              \
+                           static_cast<int>(value1_val), value2_name,       \
+                           static_cast<int>(value2_val))
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID1(category_group, name, id, value)                    \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, "value",  \
+                                   static_cast<int>(value))
+#define TRACE_COPY_COUNTER_ID1(category_group, name, id, value)               \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, "value",  \
+                                   static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID2(category_group, name, id, value1_name, value1_val,  \
+                          value2_name, value2_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE,           \
+                                   value1_name, static_cast<int>(value1_val), \
+                                   value2_name, static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER_ID2(category_group, name, id, value1_name,         \
+                               value1_val, value2_name, value2_val)           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY,           \
+                                   value1_name, static_cast<int>(value1_val), \
+                                   value2_name, static_cast<int>(value2_val))
+
+
+// Records a single ASYNC_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the ASYNC_BEGIN event with the ASYNC_END event. ASYNC
+//   events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+//
+// An asynchronous operation can consist of multiple phases. The first phase is
+// defined by the ASYNC_BEGIN calls. Additional phases can be defined using the
+// ASYNC_STEP_INTO or ASYNC_STEP_PAST macros. The ASYNC_STEP_INTO macro will
+// annotate the block following the call. The ASYNC_STEP_PAST macro will
+// annotate the block prior to the call. Note that any particular event must use
+// only STEP_INTO or STEP_PAST macros; they can not mix and match. When the
+// operation completes, call ASYNC_END.
+//
+// An ASYNC trace typically occurs on a single thread (if not, they will only be
+// drawn on the thread defined in the ASYNC_BEGIN event), but all events in that
+// operation must use the same |name| and |id|. Each step can have its own
+// args.
+#define TRACE_EVENT_ASYNC_BEGIN0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+                                   category_group, name, id,      \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_BEGIN1(category_group, name, id, arg1_name, \
+                                 arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN,     \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+                                 arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,        \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+                                   category_group, name, id,      \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN1(category_group, name, id, arg1_name, \
+                                      arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN,          \
+                                   category_group, name, id,               \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+                                      arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                        \
+      TRACE_EVENT_PHASE_ASYNC_BEGIN, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single ASYNC_STEP_INTO event for |step| immediately. If the
+// category is not enabled, then this does nothing. The |name| and |id| must
+// match the ASYNC_BEGIN event above. The |step| param identifies this step
+// within the async event. This should be called at the beginning of the next
+// phase of an asynchronous operation. The ASYNC_BEGIN event must not have any
+// ASYNC_STEP_PAST events.
+#define TRACE_EVENT_ASYNC_STEP_INTO0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP_INTO, \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_ASYNC_STEP_INTO1(category_group, name, id, step, \
+                                     arg1_name, arg1_val)            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_ASYNC_STEP_INTO, category_group, name, id,   \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+
+// Records a single ASYNC_STEP_PAST event for |step| immediately. If the
+// category is not enabled, then this does nothing. The |name| and |id| must
+// match the ASYNC_BEGIN event above. The |step| param identifies this step
+// within the async event. This should be called at the beginning of the next
+// phase of an asynchronous operation. The ASYNC_BEGIN event must not have any
+// ASYNC_STEP_INTO events.
+#define TRACE_EVENT_ASYNC_STEP_PAST0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP_PAST, \
+                                   category_group, name, id,          \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_ASYNC_STEP_PAST1(category_group, name, id, step, \
+                                     arg1_name, arg1_val)            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_ASYNC_STEP_PAST, category_group, name, id,   \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+
+// Records a single ASYNC_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_ASYNC_END0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_END1(category_group, name, id, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END,               \
+                                   category_group, name, id,                  \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_END2(category_group, name, id, arg1_name, arg1_val, \
+                               arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                           \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,                  \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_END0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_END1(category_group, name, id, arg1_name, \
+                                    arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END,          \
+                                   category_group, name, id,             \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_END2(category_group, name, id, arg1_name, \
+                                    arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                      \
+      TRACE_EVENT_PHASE_ASYNC_END, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+
+// Records a single FLOW_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the FLOW_BEGIN event with the FLOW_END event. FLOW
+//   events are considered to match if their category_group, name and id values
+//   all match. |id| must either be a pointer or an integer value up to 64 bits.
+//   If it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+// FLOW events are different from ASYNC events in how they are drawn by the
+// tracing UI. A FLOW defines asynchronous data flow, such as posting a ta
+// (FLOW_BEGIN) and later executing that ta (FLOW_END). Expect FLOWs to be
+// drawn as lines or arrows from FLOW_BEGIN scopes to FLOW_END scopes. Similar
+// to ASYNC, a FLOW can consist of multiple phases. The first phase is defined
+// by the FLOW_BEGIN calls. Additional phases can be defined using the FLOW_STEP
+// macros. When the operation completes, call FLOW_END. An async operation can
+// span threads and processes, but all events in that operation must use the
+// same |name| and |id|. Each event can have its own args.
+#define TRACE_EVENT_FLOW_BEGIN0(category_group, name, id)        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+                                   category_group, name, id,     \
+                                   TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_BEGIN1(category_group, name, id, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN,               \
+                                   category_group, name, id,                   \
+                                   TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_FLOW_BEGIN2(category_group, name, id, arg1_name, arg1_val, \
+                                arg2_name, arg2_val)                           \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_FLOW_BEGIN, category_group, name, id,                  \
+      TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN0(category_group, name, id)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+                                   category_group, name, id,     \
+                                   TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_BEGIN1(category_group, name, id, arg1_name, \
+                                     arg1_val)                            \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN,          \
+                                   category_group, name, id,              \
+                                   TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN2(category_group, name, id, arg1_name, \
+                                     arg1_val, arg2_name, arg2_val)       \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_FLOW_BEGIN, category_group, name, id,             \
+      TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single FLOW_STEP event for |step| immediately. If the category
+// is not enabled, then this does nothing. The |name| and |id| must match the
+// FLOW_BEGIN event above. The |step| param identifies this step within the
+// async event. This should be called at the beginning of the next phase of an
+// asynchronous operation.
+#define TRACE_EVENT_FLOW_STEP0(category_group, name, id, step)  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+                                   category_group, name, id,    \
+                                   TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_FLOW_STEP1(category_group, name, id, step, arg1_name, \
+                               arg1_val)                                  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                       \
+      TRACE_EVENT_PHASE_FLOW_STEP, category_group, name, id,              \
+      TRACE_EVENT_FLAG_NONE, "step", step, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_STEP0(category_group, name, id, step) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP,     \
+                                   category_group, name, id,        \
+                                   TRACE_EVENT_FLAG_COPY, "step", step)
+#define TRACE_EVENT_COPY_FLOW_STEP1(category_group, name, id, step, arg1_name, \
+                                    arg1_val)                                  \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                            \
+      TRACE_EVENT_PHASE_FLOW_STEP, category_group, name, id,                   \
+      TRACE_EVENT_FLAG_COPY, "step", step, arg1_name, arg1_val)
+
+// Records a single FLOW_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_FLOW_END0(category_group, name, id)                        \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_END1(category_group, name, id, arg1_name, arg1_val)   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, arg1_name, \
+                                   arg1_val)
+#define TRACE_EVENT_FLOW_END2(category_group, name, id, arg1_name, arg1_val,   \
+                              arg2_name, arg2_val)                             \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_NONE, arg1_name, \
+                                   arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_END0(category_group, name, id)                   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_END1(category_group, name, id, arg1_name,        \
+                                   arg1_val)                                   \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, arg1_name, \
+                                   arg1_val)
+#define TRACE_EVENT_COPY_FLOW_END2(category_group, name, id, arg1_name,        \
+                                   arg1_val, arg2_name, arg2_val)              \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, category_group, \
+                                   name, id, TRACE_EVENT_FLAG_COPY, arg1_name, \
+                                   arg1_val, arg2_name, arg2_val)
+
+// Macros to track the life time and value of arbitrary client objects.
+// See also TraceTrackableObject.
+#define TRACE_EVENT_OBJECT_CREATED_WITH_ID(category_group, name, id) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_CREATE_OBJECT, category_group, name,         \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+
+#define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(category_group, name, id, \
+                                            snapshot)                 \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,        \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
+
+#define TRACE_EVENT_OBJECT_DELETED_WITH_ID(category_group, name, id) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
+      TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name,         \
+      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+
+#define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE() \
+  *INTERNAL_TRACE_EVENT_UID(category_group_enabled) &                    \
+      (EventTracer::kEnabledForRecording_CategoryGroupEnabledFlags |     \
+       EventTracer::kEnabledForEventCallback_CategoryGroupEnabledFlags)
+
+// Macro to efficiently determine if a given category group is enabled.
+#define TRACE_EVENT_CATEGORY_GROUP_ENABLED(category_group, ret)             \
+  do {                                                                      \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                 \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+      *ret = true;                                                          \
+    } else {                                                                \
+      *ret = false;                                                         \
+    }                                                                       \
+  } while (0)
+
+// Macro to efficiently determine, through polling, if a new trace has begun.
+#define TRACE_EVENT_IS_NEW_TRACE(ret)                                      \
+  do {                                                                     \
+    static int INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = 0;          \
+    int num_traces_recorded = TRACE_EVENT_API_GET_NUM_TRACES_RECORDED();   \
+    if (num_traces_recorded != -1 &&                                       \
+        num_traces_recorded !=                                             \
+            INTERNAL_TRACE_EVENT_UID(lastRecordingNumber)) {               \
+      INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = num_traces_recorded; \
+      *ret = true;                                                         \
+    } else {                                                               \
+      *ret = false;                                                        \
+    }                                                                      \
+  } while (0)
+
+////////////////////////////////////////////////////////////////////////////////
+// Implementation specific tracing API definitions.
+
+// Get a pointer to the enabled state of the given trace category. Only
+// long-lived literal strings should be given as the category group. The
+// returned pointer can be held permanently in a local static for example. If
+// the unsigned char is non-zero, tracing is enabled. If tracing is enabled,
+// TRACE_EVENT_API_ADD_TRACE_EVENT can be called. It's OK if tracing is disabled
+// between the load of the tracing state and the call to
+// TRACE_EVENT_API_ADD_TRACE_EVENT, because this flag only provides an early out
+// for best performance when tracing is disabled.
+// const uint8_t*
+//     TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(const char* category_group)
+#define TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED \
+  EventTracer::GetInstance()->getCategoryGroupEnabled
+
+// Get the number of times traces have been recorded. This is used to implement
+// the TRACE_EVENT_IS_NEW_TRACE facility.
+// unsigned int TRACE_EVENT_API_GET_NUM_TRACES_RECORDED()
+#define TRACE_EVENT_API_GET_NUM_TRACES_RECORDED \
+  EventTracer::GetInstance()->getNumTracesRecorded
+
+// Add a trace event to the platform tracing system.
+// EventTracer::Handle TRACE_EVENT_API_ADD_TRACE_EVENT(
+//                    char phase,
+//                    const uint8_t* category_group_enabled,
+//                    const char* name,
+//                    uint64_t id,
+//                    int num_args,
+//                    const char** arg_names,
+//                    const uint8_t* arg_types,
+//                    const uint64_t* arg_values,
+//                    unsigned char flags)
+#define TRACE_EVENT_API_ADD_TRACE_EVENT \
+  EventTracer::GetInstance()->addTraceEvent
+
+// Set the duration field of a COMPLETE trace event.
+// void TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+//     const uint8_t* category_group_enabled,
+//     const char* name,
+//     EventTracer::Handle id)
+#define TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION \
+  EventTracer::GetInstance()->updateTraceEventDuration
+
+// These operations are atomic in the Chrome tracing implementation
+// to cater to ARM's weak memory consistency; we're just doing read/
+// write here because it's not strictly needed for correctness.
+// So says Nat.
+// FIXME
+
+#define TRACE_EVENT_API_ATOMIC_WORD intptr_t
+#define TRACE_EVENT_API_ATOMIC_LOAD(var) (*(&var))
+#define TRACE_EVENT_API_ATOMIC_STORE(var, value) (var = value)
+
+// Defines visibility for classes in trace_event.h
+// #define TRACE_EVENT_API_CLASS_EXPORT _API
+
+// The thread buckets for the sampling profiler.
+extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state[3];
+
+#define TRACE_EVENT_API_THREAD_BUCKET(thread_bucket) \
+  g_trace_state[thread_bucket]
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Implementation detail: trace event macros create temporary variables
+// to keep instrumentation overhead low. These macros give each temporary
+// variable a unique name based on the line number to prevent name collisions.
+#define INTERNAL_TRACE_EVENT_UID3(a, b) trace_event_unique_##a##b
+#define INTERNAL_TRACE_EVENT_UID2(a, b) INTERNAL_TRACE_EVENT_UID3(a, b)
+#define INTERNAL_TRACE_EVENT_UID(name_prefix) \
+  INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
+
+// Implementation detail: internal macro to create static category.
+// No barriers are needed, because this code is designed to operate safely
+// even when the unsigned char* points to garbage data (which may be the case
+// on processors without cache coherency).
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(             \
+    category_group, atomic, category_group_enabled)                          \
+  category_group_enabled =                                                   \
+      reinterpret_cast<const uint8_t*>(TRACE_EVENT_API_ATOMIC_LOAD(atomic)); \
+  if (!category_group_enabled) {                                             \
+    category_group_enabled =                                                 \
+        TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(category_group);          \
+    TRACE_EVENT_API_ATOMIC_STORE(                                            \
+        atomic, reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(               \
+                    category_group_enabled));                                \
+  }
+
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group)             \
+  static TRACE_EVENT_API_ATOMIC_WORD INTERNAL_TRACE_EVENT_UID(atomic) = 0; \
+  const uint8_t* INTERNAL_TRACE_EVENT_UID(category_group_enabled);         \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(                 \
+      category_group, INTERNAL_TRACE_EVENT_UID(atomic),                    \
+      INTERNAL_TRACE_EVENT_UID(category_group_enabled));
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD(phase, category_group, name, ...)          \
+  do {                                                                      \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                 \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+      v8::tracing_internals::AddTraceEvent(                                 \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,    \
+          v8::tracing_internals::kNoEventId, __VA_ARGS__);                  \
+    }                                                                       \
+  } while (0)
+
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, ...)        \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                 \
+  v8::tracing_internals::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer);   \
+  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+    EventTracer::Handle h = v8::tracing_internals::AddTraceEvent(         \
+        TRACE_EVENT_PHASE_COMPLETE,                                       \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,           \
+        v8::tracing_internals::kNoEventId, TRACE_EVENT_FLAG_NONE,         \
+        __VA_ARGS__);                                                     \
+    INTERNAL_TRACE_EVENT_UID(tracer).Initialize(                          \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, h);       \
+  }
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category_group, name, id,      \
+                                         flags, ...)                           \
+  do {                                                                         \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                    \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {    \
+      unsigned char trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID;       \
+      v8::tracing_internals::TraceID trace_event_trace_id(id,                  \
+                                                          &trace_event_flags); \
+      v8::tracing_internals::AddTraceEvent(                                    \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,       \
+          trace_event_trace_id.data(), trace_event_flags, __VA_ARGS__);        \
+    }                                                                          \
+  } while (0)
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                    \
+    phase, category_group, name, id, thread_id, flags, ...)                    \
+  do {                                                                         \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                    \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {    \
+      unsigned char trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID;       \
+      v8::tracing_internals::TraceID trace_event_trace_id(id,                  \
+                                                          &trace_event_flags); \
+      v8::tracing_internals::AddTraceEventWithThreadIdAndTimestamp(            \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,       \
+          trace_event_trace_id.data(), thread_id,                              \
+          base::TimeTicks::FromInternalValue(timestamp), trace_event_flags,    \
+          __VA_ARGS__);                                                        \
+    }                                                                          \
+  } while (0)
+
+// Notes regarding the following definitions:
+// New values can be added and propagated to third party libraries, but existing
+// definitions must never be changed, because third party libraries may use old
+// definitions.
+
+// Phase indicates the nature of an event entry. E.g. part of a begin/end pair.
+#define TRACE_EVENT_PHASE_BEGIN ('B')
+#define TRACE_EVENT_PHASE_END ('E')
+#define TRACE_EVENT_PHASE_COMPLETE ('X')
+#define TRACE_EVENT_PHASE_INSTANT ('i')
+#define TRACE_EVENT_PHASE_ASYNC_BEGIN ('S')
+#define TRACE_EVENT_PHASE_ASYNC_STEP_INTO ('T')
+#define TRACE_EVENT_PHASE_ASYNC_STEP_PAST ('p')
+#define TRACE_EVENT_PHASE_ASYNC_END ('F')
+#define TRACE_EVENT_PHASE_FLOW_BEGIN ('s')
+#define TRACE_EVENT_PHASE_FLOW_STEP ('t')
+#define TRACE_EVENT_PHASE_FLOW_END ('f')
+#define TRACE_EVENT_PHASE_METADATA ('M')
+#define TRACE_EVENT_PHASE_COUNTER ('C')
+#define TRACE_EVENT_PHASE_SAMPLE ('P')
+#define TRACE_EVENT_PHASE_CREATE_OBJECT ('N')
+#define TRACE_EVENT_PHASE_SNAPSHOT_OBJECT ('O')
+#define TRACE_EVENT_PHASE_DELETE_OBJECT ('D')
+
+// Flags for changing the behavior of TRACE_EVENT_API_ADD_TRACE_EVENT.
+#define TRACE_EVENT_FLAG_NONE (static_cast<unsigned char>(0))
+#define TRACE_EVENT_FLAG_COPY (static_cast<unsigned char>(1 << 0))
+#define TRACE_EVENT_FLAG_HAS_ID (static_cast<unsigned char>(1 << 1))
+#define TRACE_EVENT_FLAG_MANGLE_ID (static_cast<unsigned char>(1 << 2))
+#define TRACE_EVENT_FLAG_SCOPE_OFFSET (static_cast<unsigned char>(1 << 3))
+
+#define TRACE_EVENT_FLAG_SCOPE_MA                             \
+  (static_cast<unsigned char>(TRACE_EVENT_FLAG_SCOPE_OFFSET | \
+                              (TRACE_EVENT_FLAG_SCOPE_OFFSET << 1)))
+
+// Type values for identifying types in the TraceValue union.
+#define TRACE_VALUE_TYPE_BOOL (static_cast<unsigned char>(1))
+#define TRACE_VALUE_TYPE_UINT (static_cast<unsigned char>(2))
+#define TRACE_VALUE_TYPE_INT (static_cast<unsigned char>(3))
+#define TRACE_VALUE_TYPE_DOUBLE (static_cast<unsigned char>(4))
+#define TRACE_VALUE_TYPE_POINTER (static_cast<unsigned char>(5))
+#define TRACE_VALUE_TYPE_STRING (static_cast<unsigned char>(6))
+#define TRACE_VALUE_TYPE_COPY_STRING (static_cast<unsigned char>(7))
+#define TRACE_VALUE_TYPE_CONVERTABLE (static_cast<unsigned char>(8))
+
+// Enum reflecting the scope of an INSTANT event. Must fit within
+// TRACE_EVENT_FLAG_SCOPE_MA.
+#define TRACE_EVENT_SCOPE_GLOBAL (static_cast<unsigned char>(0 << 3))
+#define TRACE_EVENT_SCOPE_PROCESS (static_cast<unsigned char>(1 << 3))
+#define TRACE_EVENT_SCOPE_THREAD (static_cast<unsigned char>(2 << 3))
+
+#define TRACE_EVENT_SCOPE_NAME_GLOBAL ('g')
+#define TRACE_EVENT_SCOPE_NAME_PROCESS ('p')
+#define TRACE_EVENT_SCOPE_NAME_THREAD ('t')
+
+namespace v8 {
+namespace tracing_internals {
+
+// Specify these values when the corresponding argument of AddTraceEvent is not
+// used.
+const int kZeroNumArgs = 0;
+const uint64_t kNoEventId = 0;
+
+// TraceID encapsulates an ID that can either be an integer or pointer. Pointers
+// are by default mangled with the Process ID so that they are unlikely to
+// collide when the same pointer is used on different processes.
+class TraceID {
+ public:
+  class DontMangle {
+   public:
+    explicit DontMangle(const void* id)
+        : data_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(id))) {}
+    explicit DontMangle(uint64_t id) : data_(id) {}
+    explicit DontMangle(unsigned int id) : data_(id) {}
+    explicit DontMangle(uint16_t id) : data_(id) {}
+    explicit DontMangle(unsigned char id) : data_(id) {}
+    explicit DontMangle(int64_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(int id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(int16_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(signed char id) : data_(static_cast<uint64_t>(id)) {}
+    uint64_t data() const { return data_; }
+
+   private:
+    uint64_t data_;
+  };
+
+  class ForceMangle {
+   public:
+    explicit ForceMangle(uint64_t id) : data_(id) {}
+    explicit ForceMangle(unsigned int id) : data_(id) {}
+    explicit ForceMangle(uint16_t id) : data_(id) {}
+    explicit ForceMangle(unsigned char id) : data_(id) {}
+    explicit ForceMangle(int64_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(int id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(int16_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(signed char id) : data_(static_cast<uint64_t>(id)) {}
+    uint64_t data() const { return data_; }
+
+   private:
+    uint64_t data_;
+  };
+
+  TraceID(const void* id, unsigned char* flags)
+      : data_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(id))) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(ForceMangle id, unsigned char* flags) : data_(id.data()) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(DontMangle id, unsigned char* flags) : data_(id.data()) {}
+  TraceID(uint64_t id, unsigned char* flags) : data_(id) { (void)flags; }
+  TraceID(unsigned int id, unsigned char* flags) : data_(id) { (void)flags; }
+  TraceID(uint16_t id, unsigned char* flags) : data_(id) { (void)flags; }
+  TraceID(unsigned char id, unsigned char* flags) : data_(id) { (void)flags; }
+  TraceID(int64_t id, unsigned char* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(int id, unsigned char* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(int16_t id, unsigned char* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(signed char id, unsigned char* flags)
+      : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+
+  uint64_t data() const { return data_; }
+
+ private:
+  uint64_t data_;
+};
+
+// Simple union to store various types as uint64_t.
+union TraceValueUnion {
+  bool as_bool;
+  uint64_t as_uint;
+  int64_t as_int;
+  double as_double;
+  const void* as_pointer;
+  const char* as_string;
+};
+
+// Simple container for const char* that should be copied instead of retained.
+class TraceStringWithCopy {
+ public:
+  explicit TraceStringWithCopy(const char* str) : str_(str) {}
+  operator const char*() const { return str_; }
+
+ private:
+  const char* str_;
+};
+
+// Define SetTraceValue for each allowed type. It stores the type and
+// value in the return arguments. This allows this API to avoid declaring any
+// structures so that it is portable to third_party libraries.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE(actual_type, union_member,      \
+                                         value_type_id)                  \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                   uint64_t* value) {                    \
+    TraceValueUnion type_value;                                          \
+    type_value.union_member = arg;                                       \
+    *type = value_type_id;                                               \
+    *value = type_value.as_uint;                                         \
+  }
+// Simpler form for int types that can be safely casted.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE_INT(actual_type, value_type_id) \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                   uint64_t* value) {                    \
+    *type = value_type_id;                                               \
+    *value = static_cast<uint64_t>(arg);                                 \
+  }
+
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint64_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned int, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint16_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned char, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int64_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int16_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(signed char, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE(bool, as_bool, TRACE_VALUE_TYPE_BOOL)
+INTERNAL_DECLARE_SET_TRACE_VALUE(double, as_double, TRACE_VALUE_TYPE_DOUBLE)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const void*, as_pointer,
+                                 TRACE_VALUE_TYPE_POINTER)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const char*, as_string,
+                                 TRACE_VALUE_TYPE_STRING)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const TraceStringWithCopy&, as_string,
+                                 TRACE_VALUE_TYPE_COPY_STRING)
+
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE_INT
+
+// These AddTraceEvent and AddTraceEvent template
+// functions are defined here instead of in the macro, because the arg_values
+// could be temporary objects, such as std::string. In order to store
+// pointers to the internal c_str and pass through to the tracing API,
+// the arg_values must live throughout these procedures.
+
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, unsigned char flags) {
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(phase, category_group_enabled, name,
+                                         id, kZeroNumArgs, NULL, NULL, NULL,
+                                         flags);
+}
+
+template <class ARG1_TYPE>
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, unsigned char flags, const char* arg1_name,
+    const ARG1_TYPE& arg1_val) {
+  const int num_args = 1;
+  uint8_t arg_types[1];
+  uint64_t arg_values[1];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(phase, category_group_enabled, name,
+                                         id, num_args, &arg1_name, arg_types,
+                                         arg_values, flags);
+}
+
+template <class ARG1_TYPE, class ARG2_TYPE>
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, unsigned char flags, const char* arg1_name,
+    const ARG1_TYPE& arg1_val, const char* arg2_name,
+    const ARG2_TYPE& arg2_val) {
+  const int num_args = 2;
+  const char* arg_names[2] = {arg1_name, arg2_name};
+  unsigned char arg_types[2];
+  uint64_t arg_values[2];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(phase, category_group_enabled, name,
+                                         id, num_args, arg_names, arg_types,
+                                         arg_values, flags);
+}
+
+// Used by TRACE_EVENTx macros. Do not use directly.
+class ScopedTracer {
+ public:
+  // Note: members of data_ intentionally left uninitialized. See Initialize.
+  ScopedTracer() : p_data_(NULL) {}
+
+  ~ScopedTracer() {
+    if (p_data_ && *data_.category_group_enabled)
+      TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+          data_.category_group_enabled, data_.name, data_.event_handle);
+  }
+
+  void Initialize(const uint8_t* category_group_enabled, const char* name,
+                  EventTracer::Handle event_handle) {
+    data_.category_group_enabled = category_group_enabled;
+    data_.name = name;
+    data_.event_handle = event_handle;
+    p_data_ = &data_;
+  }
+
+ private:
+  // This Data struct workaround is to avoid initializing all the members
+  // in Data during construction of this object, since this object is always
+  // constructed, even when tracing is disabled. If the members of Data were
+  // members of this class instead, compiler warnings occur about potential
+  // uninitialized accesses.
+  struct Data {
+    const uint8_t* category_group_enabled;
+    const char* name;
+    EventTracer::Handle event_handle;
+  };
+  Data* p_data_;
+  Data data_;
+};
+
+// Used by TRACE_EVENT_BINARY_EFFICIENTx macro. Do not use directly.
+class ScopedTraceBinaryEfficient {
+ public:
+  ScopedTraceBinaryEfficient(const char* category_group, const char* name);
+  ~ScopedTraceBinaryEfficient();
+
+ private:
+  const uint8_t* category_group_enabled_;
+  const char* name_;
+  EventTracer::Handle event_handle_;
+};
+
+// This macro generates less code then TRACE_EVENT0 but is also
+// slower to execute when tracing is off. It should generally only be
+// used with code that is seldom executed or conditionally executed
+// when debugging.
+// For now the category_group must be "gpu".
+#define TRACE_EVENT_BINARY_EFFICIENT0(category_group, name)                   \
+  v8::tracing_internals::ScopedTraceBinaryEfficient INTERNAL_TRACE_EVENT_UID( \
+      scoped_trace)(category_group, name);
+
+// TraceEventSamplingStateScope records the current sampling state
+// and sets a new sampling state. When the scope exists, it restores
+// the sampling state having recorded.
+template <size_t BucketNumber>
+class TraceEventSamplingStateScope {
+ public:
+  explicit TraceEventSamplingStateScope(const char* category_and_name) {
+    previous_state_ = TraceEventSamplingStateScope<BucketNumber>::Current();
+    TraceEventSamplingStateScope<BucketNumber>::Set(category_and_name);
+  }
+
+  ~TraceEventSamplingStateScope() {
+    TraceEventSamplingStateScope<BucketNumber>::Set(previous_state_);
+  }
+
+  static inline const char* Current() {
+    return reinterpret_cast<const char*>(
+        TRACE_EVENT_API_ATOMIC_LOAD(g_trace_state[BucketNumber]));
+  }
+
+  static inline void Set(const char* category_and_name) {
+    TRACE_EVENT_API_ATOMIC_STORE(g_trace_state[BucketNumber],
+                                 reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(
+                                     const_cast<char*>(category_and_name)));
+  }
+
+ private:
+  const char* previous_state_;
+};
+
+}  // namespace tracing_internals
+}  // namespace v8
+
+#endif  // SRC_TRACING_TRACE_EVENT_H_