tracing: Simplify TraceEventMemoryOverhead, use an enum insted of a map

base/trace_event/trace_event_impl.cc

 // 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.
 
 #include "base/trace_event/trace_event_impl.h"
 
 #include <stddef.h>
 
 #include "base/format_macros.h"
 #include "base/json/string_escape.h"
@@ skipping 180 matching lines @@
   duration_ = now - timestamp_;
 
   // |thread_timestamp_| can be empty if the thread ticks clock wasn't
   // initialized when it was recorded.
   if (thread_timestamp_ != ThreadTicks())
     thread_duration_ = thread_now - thread_timestamp_;
 }
 
 void TraceEvent::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
-  overhead->Add("TraceEvent", sizeof(*this));
+  overhead->Add(TraceEventMemoryOverhead::kTraceEvent, sizeof(*this));
 
   if (parameter_copy_storage_)
     overhead->AddString(*parameter_copy_storage_);
 
   for (size_t i = 0; i < kTraceMaxNumArgs; ++i) {
     if (arg_types_[i] == TRACE_VALUE_TYPE_CONVERTABLE)
       convertable_values_[i]->EstimateTraceMemoryOverhead(overhead);
   }
 }
 
@@ skipping 269 matching lines @@
         base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
   }
 
   if (id_flags_ != TRACE_EVENT_FLAG_HAS_ID)
     value->EndDictionary();
 
   return std::move(value);
 }
 
 }  // namespace trace_event_internal