[ETW Export] Add polling for ETW keyword.

base/trace_event/trace_log.h

Index: base/trace_event/trace_log.h
diff --git a/base/trace_event/trace_log.h b/base/trace_event/trace_log.h
index 510113ae11fa6c9887a1ed050b235d2f4091bb31..8d6dec30ca168b1cfc01f21b285e87a666eaf2cf 100644
--- a/base/trace_event/trace_log.h
+++ b/base/trace_event/trace_log.h
@@ -326,6 +326,10 @@ class BASE_EXPORT TraceLog : public MemoryDumpProvider {
   // by the Singleton class.
   friend struct DefaultSingletonTraits<TraceLog>;
 
+  // This allows TraceEventETWExport to call UpdateCategoryGroupEnabledFlags
+  // whenever required (ie. when ETW keyword changes).
+  friend class TraceEventETWExport;

[dsinclair, 2015/08/11 19:33:14]

This is kinda gross as it gives access to everything. Should the mentioned
method be public? Or is there a better api to call to do the  updating?

[Georges Khalil, 2015/08/12 17:24:25]

I added an API in tracelog that allows us to set/clear just the ETW bit in the
categories. I also now acquire the internal lock to avoid any potential race
condition.

+
   // MemoryDumpProvider implementation.
   bool OnMemoryDump(const MemoryDumpArgs& args,
                     ProcessMemoryDump* pmd) override;