[tracing] Add trace events to key heap profiler functions.

base/trace_event/heap_profiler_string_deduplicator.cc

 // Copyright 2017 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.
 
 #include "base/trace_event/heap_profiler_string_deduplicator.h"
 
 #include "base/trace_event/memory_usage_estimator.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "base/trace_event/trace_event_memory_overhead.h"
@@ skipping 20 matching lines @@
   // Insert new mapping. Note that |string_ids_| keys reference values
   // from |strings_|.
   int string_id = static_cast<int>(strings_.size());
   strings_.push_back(string.as_string());
   auto iter_and_flag = string_ids_.insert({strings_.back(), string_id});
   DCHECK(iter_and_flag.second);  // insert() must succeed
   return string_id;
 }
 
 void StringDeduplicator::SerializeIncrementally(TracedValue* traced_value) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("memory-infra"),
+               "StringDeduplicator::SerializeIncrementally");
   for (; last_serialized_index_ != strings_.size(); ++last_serialized_index_) {
     traced_value->BeginDictionary();
     traced_value->SetInteger("id", last_serialized_index_);
     traced_value->SetString("string", strings_[last_serialized_index_]);
     traced_value->EndDictionary();
   }
 }
 
 void StringDeduplicator::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
   size_t memory_usage =
       EstimateMemoryUsage(string_ids_) + EstimateMemoryUsage(strings_);
   overhead->Add(TraceEventMemoryOverhead::kHeapProfilerStringDeduplicator,
                 sizeof(StringDeduplicator) + memory_usage);
 }
 
 }  // namespace trace_event
 }  // namespace base