Update from https://crrev.com/327068

base/trace_event/trace_event_impl.h

Index: base/trace_event/trace_event_impl.h
diff --git a/base/trace_event/trace_event_impl.h b/base/trace_event/trace_event_impl.h
index efa20c4ff85ff57b3b6c52b22247cfb136392fe6..33a85c9b6ce854f4e6b6cde748fe6abca8a015d2 100644
--- a/base/trace_event/trace_event_impl.h
+++ b/base/trace_event/trace_event_impl.h
@@ -26,6 +26,7 @@
 
 // Older style trace macros with explicit id and extra data
 // Only these macros result in publishing data to ETW as currently implemented.
+// TODO(georgesak): Update/replace these with new ETW macros.
 #define TRACE_EVENT_BEGIN_ETW(name, id, extra) \
     base::trace_event::TraceLog::AddTraceEventEtw( \
         TRACE_EVENT_PHASE_BEGIN, \
@@ -446,6 +447,8 @@ class BASE_EXPORT TraceLog {
     ENABLED_FOR_MONITORING = 1 << 1,
     // Category group enabled by SetEventCallbackEnabled().
     ENABLED_FOR_EVENT_CALLBACK = 1 << 2,
+    // Category group enabled to export events to ETW.
+    ENABLED_FOR_ETW_EXPORT = 1 << 3
   };
 
   static TraceLog* GetInstance();
@@ -538,10 +541,11 @@ class BASE_EXPORT TraceLog {
   // Due to the implementation of thread-local buffers, flush can't be
   // done when tracing is enabled. If called when tracing is enabled, the
   // callback will be called directly with (empty_string, false) to indicate
-  // the end of this unsuccessful flush.
+  // the end of this unsuccessful flush. Flush does the serialization
+  // on the same thread if the caller doesn't set use_worker_thread explicitly.
   typedef base::Callback<void(const scoped_refptr<base::RefCountedString>&,
                               bool has_more_events)> OutputCallback;
-  void Flush(const OutputCallback& cb);
+  void Flush(const OutputCallback& cb, bool use_worker_thread = false);
   void FlushButLeaveBufferIntact(const OutputCallback& flush_output_callback);
 
   // Called by TRACE_EVENT* macros, don't call this directly.
@@ -602,6 +606,8 @@ class BASE_EXPORT TraceLog {
 
   int process_id() const { return process_id_; }
 
+  uint64 MangleEventId(uint64 id);
+
   // Exposed for unittesting:
 
   void WaitSamplingEventForTesting();
@@ -710,7 +716,9 @@ class BASE_EXPORT TraceLog {
   // |generation| is used in the following callbacks to check if the callback
   // is called for the flush of the current |logged_events_|.
   void FlushCurrentThread(int generation);
-  void ConvertTraceEventsToTraceFormat(scoped_ptr<TraceBuffer> logged_events,
+  // Usually it runs on a different thread.
+  static void ConvertTraceEventsToTraceFormat(
+      scoped_ptr<TraceBuffer> logged_events,
       const TraceLog::OutputCallback& flush_output_callback);
   void FinishFlush(int generation);
   void OnFlushTimeout(int generation);
@@ -803,6 +811,7 @@ class BASE_EXPORT TraceLog {
   OutputCallback flush_output_callback_;
   scoped_refptr<MessageLoopProxy> flush_message_loop_proxy_;
   subtle::AtomicWord generation_;
+  bool use_worker_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };