Don't use PostTask queueing between compositor and main thread.

content/renderer/input/input_handler_manager_client.h

Index: content/renderer/input/input_handler_manager_client.h
diff --git a/content/renderer/input/input_handler_manager_client.h b/content/renderer/input/input_handler_manager_client.h
index c6e3a708b3f97e5933c6bbe633dbecaa2a49f05f..e3da89650408153943223f609c04beb199d304ab 100644
--- a/content/renderer/input/input_handler_manager_client.h
+++ b/content/renderer/input/input_handler_manager_client.h
@@ -42,6 +42,9 @@ class CONTENT_EXPORT InputHandlerManagerClient {
 
   // Called from the main thread.
   virtual void SetBoundHandler(const Handler& handler) = 0;
+  virtual void NotifyInputEventHandled(int routing_id,
+                                       blink::WebInputEvent::Type type,
+                                       InputEventAckState ack_result) = 0;
 
   // Called from the compositor thread.
   virtual void RegisterRoutingID(int routing_id) = 0;
@@ -50,9 +53,6 @@ class CONTENT_EXPORT InputHandlerManagerClient {
                              const DidOverscrollParams& params) = 0;
   virtual void DidStartFlinging(int routing_id) = 0;
   virtual void DidStopFlinging(int routing_id) = 0;
-  virtual void NotifyInputEventHandled(int routing_id,
-                                       blink::WebInputEvent::Type type,
-                                       InputEventAckState ack_result) = 0;
 
  protected:
   InputHandlerManagerClient() {}