Blimp Client: add support for tap gesture events

blimp/engine/session/blimp_engine_session.cc

Index: blimp/engine/session/blimp_engine_session.cc
diff --git a/blimp/engine/session/blimp_engine_session.cc b/blimp/engine/session/blimp_engine_session.cc
index 037f3e809d30393841b0a99c16204d2f07593f35..655e5d699f947511c24ec415db0a480058def8f0 100644
--- a/blimp/engine/session/blimp_engine_session.cc
+++ b/blimp/engine/session/blimp_engine_session.cc
@@ -389,7 +389,7 @@ void BlimpEngineSession::OnWebGestureEvent(
     content::RenderWidgetHost* render_widget_host,
     std::unique_ptr<blink::WebGestureEvent> event) {
   TRACE_EVENT0("blimp", "BlimpEngineSession::OnWebGestureEvent");
-
+  DVLOG(2) << "OnWebGestureEvent: " << event->type;

[Kevin M, 2016/05/16 18:31:32]

As long as we are adding traces for this event, what about just pushing
event->type in as a trace ID?

[haibinlu, 2016/05/16 18:41:42]

but trace ID does not give a sequence of event types that lead to engine crash. 

[haibinlu, 2016/05/16 18:57:29]

done

   render_widget_host->ForwardGestureEvent(*event);
 }