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

base/trace_event/heap_profiler_string_deduplicator.cc

Index: base/trace_event/heap_profiler_string_deduplicator.cc
diff --git a/base/trace_event/heap_profiler_string_deduplicator.cc b/base/trace_event/heap_profiler_string_deduplicator.cc
index bf035a19c03044b5cf675d77caa85ff65ea292db..5938e306175e77a5c105ac718f3ed5b1b307cad5 100644
--- a/base/trace_event/heap_profiler_string_deduplicator.cc
+++ b/base/trace_event/heap_profiler_string_deduplicator.cc
@@ -38,6 +38,8 @@ int StringDeduplicator::Insert(StringPiece string) {
 }
 
 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_);