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

base/trace_event/trace_log.cc

Index: base/trace_event/trace_log.cc
diff --git a/base/trace_event/trace_log.cc b/base/trace_event/trace_log.cc
index 5cdf53539231e22a877c1933f96f3a42e28b4152..d1e0fc3839bec77c7ea07f97269fc9b79bf6eb8f 100644
--- a/base/trace_event/trace_log.cc
+++ b/base/trace_event/trace_log.cc
@@ -398,7 +398,7 @@ bool TraceLog::OnMemoryDump(const MemoryDumpArgs& args,
   // TODO(ssid): Use MemoryDumpArgs to create light dumps when requested
   // (crbug.com/499731).
   TraceEventMemoryOverhead overhead;
-  overhead.Add("TraceLog", sizeof(*this));
+  overhead.Add(TraceEventMemoryOverhead::kOther, sizeof(*this));
   {
     AutoLock lock(lock_);
     if (logged_events_)
@@ -1678,7 +1678,8 @@ void TraceLog::UpdateETWCategoryGroupEnabledFlags() {
 
 void ConvertableToTraceFormat::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
-  overhead->Add("ConvertableToTraceFormat(Unknown)", sizeof(*this));
+  overhead->Add(TraceEventMemoryOverhead::kConvertableToTraceFormat,
+                sizeof(*this));
 }
 
 void TraceLog::AddAsyncEnabledStateObserver(