[ETW Export] Add polling for ETW keyword.

base/trace_event/trace_log.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_LOG_H_
 #define BASE_TRACE_EVENT_TRACE_LOG_H_
 
 #include "base/trace_event/memory_dump_provider.h"
 #include "base/trace_event/trace_config.h"
 #include "base/trace_event/trace_event_impl.h"
@@ skipping 289 matching lines @@
   // that should be reported.
   void SetTimeOffset(TimeDelta offset);
 
   size_t GetObserverCountForTest() const;
 
   // Call this method if the current thread may block the message loop to
   // prevent the thread from using the thread-local buffer because the thread
   // may not handle the flush request in time causing lost of unflushed events.
   void SetCurrentThreadBlocksMessageLoop();
 
+#if defined(OS_WIN)
+  // This function is called by the ETW exporting module whenever the ETW
+  // keyword (flags) changes. This keyword indicates which categories should be
+  // exported, so whenever it changes, we adjust accordingly.
+  void UpdateETWCategoryGroupEnabledFlags();
+#endif
+
  private:
   typedef unsigned int InternalTraceOptions;
 
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture,
                            TraceBufferRingBufferGetReturnChunk);
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture,
                            TraceBufferRingBufferHalfIteration);
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture,
                            TraceBufferRingBufferFullIteration);
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture, TraceBufferVectorReportFull);
@@ skipping 158 matching lines @@
   subtle::AtomicWord generation_;
   bool use_worker_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_LOG_H_