Remove Blink's ConvertableToTraceFormat

third_party/WebKit/Source/platform/TraceEventCommon.h

 // Copyright 2015 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 119 matching lines @@
 //                  "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"));
 //
 //
 // Convertable notes:
-// Converting a large data type to a string can be costly. To help with this,
-// the trace framework provides an interface ConvertableToTraceFormat. If you
-// inherit from it and implement the AppendAsTraceFormat method the trace
-// framework will call back to your object to convert a trace output time. This
-// means, if the category for the event is disabled, the conversion will not
-// happen.
+// Unlike base's trace framework, no convertable support in Blink because of
+// the way we estimate tracing memory overhead. All objects passed to the
+// tracing framework should be allocated by malloc to calculate overhead
+// correctly, while many Blink objects use PartitionAlloc/Oilpan. Convertable
+// is an interface to avoid unnecessary conversion but if we allow to use
+// PartitionAlloc/Oilpan backed objects, overhead estimation could be wrong.
+// For structured objects, you can use TracedValue.
 //
-//   class MyData : public base::trace_event::ConvertableToTraceFormat {
+//   class MyData {
 //    public:
 //     MyData() {}
-//     void AppendAsTraceFormat(std::string* out) const override {
-//       out->append("{\"foo\":1}");
+//     PassRefPtr<TracedValue> toTracedValue() {
+//       RefPtr<TracedValue> tracedValue = TracedValue::create();
+//       tracedValue->setInteger("foo", 1);
+//       tracedValue->beginArray("bar");
+//       tracedValue->pushInteger(2);
+//       tracedValue->pushInteger(3);
+//       tracedValue->endArray();
+//       return tracedValue.release();
 //     }
 //    private:
 //     ~MyData() override {}
-//     DISALLOW_COPY_AND_ASSIGN(MyData);
 //   };
 //
-//   TRACE_EVENT1("foo", "bar", "data",
-//                scoped_refptr<ConvertableToTraceFormat>(new MyData()));
+//   TRACE_EVENT1("foo", "bar", "data", myData.toTracedValue());
 //
-// The trace framework will take ownership if the passed pointer and it will
-// be free'd when the trace buffer is flushed.
-//
-// Note, we only do the conversion when the buffer is flushed, so the provided
-// data object should not be modified after it's passed to the trace framework.
+// The trace framework will take ownership.
 //
 //
 // 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
@@ skipping 871 matching lines @@
 
 // Enum reflecting the scope of an INSTANT event. Must fit within
 // TRACE_EVENT_FLAG_SCOPE_MASK.
 #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')