implement SetWatchEvent and WaitForEvent for trace-based-tests

content/public/browser/trace_controller.h

Index: content/public/browser/trace_controller.h
diff --git a/content/public/browser/trace_controller.h b/content/public/browser/trace_controller.h
index 49670f240aba4405c24f0211827b94a4bcbdc9ec..feb99f5f550be9aa642d7eba212ac2cec9dcf175 100644
--- a/content/public/browser/trace_controller.h
+++ b/content/public/browser/trace_controller.h
@@ -70,6 +70,20 @@ class TraceController {
   //   the caller is not the current subscriber.
   virtual bool GetTraceBufferPercentFullAsync(TraceSubscriber* subscriber) = 0;
 
+  // After |num_occurrences| of given event have been seen on a particular
+  // process, |subscriber->OnEventWatchNotification()| will be called. The event
+  // count is not distributed across processes, so |num_occurrences| must occur
+  // on one process. The watch event is automatically cleared after the
+  // notification. |num_occurrences| must be greater than 0.
+  virtual bool SetWatchEvent(TraceSubscriber* subscriber,
+                             const char* category_name,
+                             const char* event_name,
+                             int num_occurrences) = 0;
+
+  // Cancel the watch event. If tracing is enabled, this may race with the
+  // watch event notification firing.
+  virtual bool CancelWatchEvent(TraceSubscriber* subscriber) = 0;
+
   // Cancel the subscriber so that it will not be called when EndTracingAsync is
   // acked by all child processes. This will also call EndTracingAsync
   // internally if necessary.