Add OnBeforeTraceLogDisabled notification to EnabledStateObserver

base/debug/trace_event_impl.h

Index: base/debug/trace_event_impl.h
diff --git a/base/debug/trace_event_impl.h b/base/debug/trace_event_impl.h
index 4cbb72144739043fe7a25f348dd6fc572ce722d5..f6fe8999c43d9df73b1e573d61e68d363aacaedf 100644
--- a/base/debug/trace_event_impl.h
+++ b/base/debug/trace_event_impl.h
@@ -502,6 +502,10 @@ class BASE_EXPORT TraceLog {
     // Called just after the tracing system disables, outside of the |lock_|.
     // TraceLog::IsEnabled() is false at this point.
     virtual void OnTraceLogDisabled() = 0;
+
+    // Called right before the tracing system disables, outside of the |lock_|.
+    // TraceLog::IsEnabled() is true at this point.
+    virtual void OnBeforeTraceLogDisabled() { }
   };
   void AddEnabledStateObserver(EnabledStateObserver* listener);
   void RemoveEnabledStateObserver(EnabledStateObserver* listener);