Added trace event for gesture scrolling.

Added instant trace event for gesture scrolls happening on compositor
thread. This existed for mouse wheel events but not gesture scrolls.

BUG=

Review URL: https://codereview.chromium.org/205893006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258949 0039d316-1c4b-4281-b951-d872f2087c98

content/renderer/input/input_handler_proxy.cc

@@ -164,6 +164,9 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleInputEvent(
         cc::InputHandler::Gesture);
     switch (scroll_status) {
       case cc::InputHandler::ScrollStarted:
+        TRACE_EVENT_INSTANT0("input",
+                             "InputHandlerProxy::handle_input gesture scroll",
+                             TRACE_EVENT_SCOPE_THREAD);
         gesture_scroll_on_impl_thread_ = true;
         return DID_HANDLE;
       case cc::InputHandler::ScrollOnMainThread: