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

base/trace_event/trace_buffer.h

 // Copyright 2015 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.
 
 #ifndef BASE_TRACE_EVENT_TRACE_BUFFER_H_
 #define BASE_TRACE_EVENT_TRACE_BUFFER_H_
 
 #include "base/base_export.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_impl.h"
@@ skipping 26 matching lines @@
   }
 
   scoped_ptr<TraceBufferChunk> Clone() const;
 
   void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead);
 
   static const size_t kTraceBufferChunkSize = 64;
 
  private:
   size_t next_free_;
-  scoped_ptr<TraceEventMemoryOverhead> cached_overhead_estimate_when_full_;
+  scoped_ptr<TraceEventMemoryOverhead> cached_overhead_estimate_;
   TraceEvent chunk_[kTraceBufferChunkSize];
   uint32 seq_;
 };
 
 // TraceBuffer holds the events as they are collected.
 class BASE_EXPORT TraceBuffer {
  public:
   virtual ~TraceBuffer() {}
 
   virtual scoped_ptr<TraceBufferChunk> GetChunk(size_t* index) = 0;
@@ skipping 59 matching lines @@
 
  private:
   OutputCallback output_callback_;
   bool append_comma_;
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_BUFFER_H_