Avoid twice clock reading

base/trace_event/trace_event.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // 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.
@@ skipping 990 matching lines @@
     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; \
         trace_event_internal::TraceID trace_event_trace_id( \
             id, &trace_event_flags); \
         trace_event_internal::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__); \
+            trace_event_flags | TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP, \
+            ##__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')
@@ skipping 16 matching lines @@
 #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_EXTRA  (static_cast<unsigned char>(1 << 4))
+#define TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP (static_cast<unsigned char>(1 << 5))
 
 #define TRACE_EVENT_FLAG_SCOPE_MASK   (static_cast<unsigned char>( \
-    TRACE_EVENT_FLAG_SCOPE_OFFSET | (TRACE_EVENT_FLAG_SCOPE_OFFSET << 1)))
+    TRACE_EVENT_FLAG_SCOPE_OFFSET | TRACE_EVENT_FLAG_SCOPE_EXTRA))
 
 // 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))
@@ skipping 536 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif /* BASE_TRACE_EVENT_TRACE_EVENT_H_ */