[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 308 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture, TraceBufferVectorReportFull);
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture,
                            ConvertTraceConfigToInternalOptions);
   FRIEND_TEST_ALL_PREFIXES(TraceEventTestFixture,
                            TraceRecordAsMuchAsPossibleMode);
 
   // This allows constructor and destructor to be private and usable only
   // by the Singleton class.
   friend struct DefaultSingletonTraits<TraceLog>;
 
+  // This allows TraceEventETWExport to call UpdateCategoryGroupEnabledFlags
+  // whenever required (ie. when ETW keyword changes).
+  friend class TraceEventETWExport;
+
   // MemoryDumpProvider implementation.
   bool OnMemoryDump(const MemoryDumpArgs& args,
                     ProcessMemoryDump* pmd) override;
 
   // Enable/disable each category group based on the current mode_,
   // category_filter_, event_callback_ and event_callback_category_filter_.
   // Enable the category group in the enabled mode if category_filter_ matches
   // the category group, or event_callback_ is not null and
   // event_callback_category_filter_ matches the category group.
   void UpdateCategoryGroupEnabledFlags();
@@ skipping 139 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_