Revert of [tracing] Fix, simplify and speed up accounting of TraceEvent memory overhead

base/trace_event/trace_event_impl.cc

Index: base/trace_event/trace_event_impl.cc
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index e78ee61b1219b18662682ec9c4e40a02b6f1c2bc..696ba66e3f31656e5fb251f1ea6ac5c92db68364 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -171,6 +171,7 @@ void TraceEvent::Reset() {
   parameter_copy_storage_ = NULL;
   for (int i = 0; i < kTraceMaxNumArgs; ++i)
     convertable_values_[i] = NULL;
+  cached_memory_overhead_estimate_.reset();
 }
 
 void TraceEvent::UpdateDuration(const TraceTicks& now,
@@ -182,18 +183,25 @@ void TraceEvent::UpdateDuration(const TraceTicks& now,
 
 void TraceEvent::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
-  overhead->Add("TraceEvent", sizeof(*this));
-
-  // TODO(primiano): parameter_copy_storage_ is refcounted and, in theory,
-  // could be shared by several events and we might overcount. In practice
-  // this is unlikely but it's worth checking.
-  if (parameter_copy_storage_)
-    overhead->AddRefCountedString(*parameter_copy_storage_.get());
-
-  for (size_t i = 0; i < kTraceMaxNumArgs; ++i) {
-    if (arg_types_[i] == TRACE_VALUE_TYPE_CONVERTABLE)
-      convertable_values_[i]->EstimateTraceMemoryOverhead(overhead);
+  if (!cached_memory_overhead_estimate_) {
+    cached_memory_overhead_estimate_.reset(new TraceEventMemoryOverhead);
+    cached_memory_overhead_estimate_->Add("TraceEvent", sizeof(*this));
+    // TODO(primiano): parameter_copy_storage_ is refcounted and, in theory,
+    // could be shared by several events and we might overcount. In practice
+    // this is unlikely but it's worth checking.
+    if (parameter_copy_storage_) {
+      cached_memory_overhead_estimate_->AddRefCountedString(
+          *parameter_copy_storage_.get());
+    }
+    for (size_t i = 0; i < kTraceMaxNumArgs; ++i) {
+      if (arg_types_[i] == TRACE_VALUE_TYPE_CONVERTABLE) {
+        convertable_values_[i]->EstimateTraceMemoryOverhead(
+            cached_memory_overhead_estimate_.get());
+      }
+    }
+    cached_memory_overhead_estimate_->AddSelf();
   }
+  overhead->Update(*cached_memory_overhead_estimate_);
 }
 
 // static