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

content/renderer/input/render_widget_input_handler.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/input/render_widget_input_handler.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <utility>
 
@@ skipping 402 matching lines @@
   if (rate_limiting_wanted && !start_time.is_null()) {
     base::TimeTicks end_time = base::TimeTicks::Now();
     total_input_handling_time_this_frame_ += (end_time - start_time);
     rate_limiting_wanted =
         total_input_handling_time_this_frame_.InMicroseconds() >
         kInputHandlingTimeThrottlingThresholdMicroseconds;
   }
 
   TRACE_EVENT_SYNTHETIC_DELAY_END("blink.HandleInputEvent");
 
-  // Note that we can't use handling_event_type_ here since it will be overriden
-  // by reentrant calls for events after the paused one.
+  // Note that we can't use handling_event_type_ here since it will be
+  // overridden by reentrant calls for events after the paused one.
   bool can_send_ack = !(ignore_ack_for_mouse_move_from_debugger_ &&
                         input_event.type == WebInputEvent::MouseMove);
-  if (dispatch_type == DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN ||
-      dispatch_type == DISPATCH_TYPE_NON_BLOCKING_NOTIFY_MAIN) {
+  if (dispatch_type == DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN) {
     // |non_blocking| means it was ack'd already by the InputHandlerProxy
     // so let the delegate know the event has been handled.
     delegate_->NotifyInputEventHandled(input_event.type, ack_result);
   }
 
   if ((dispatch_type == DISPATCH_TYPE_BLOCKING ||
        dispatch_type == DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN) &&
       can_send_ack) {
     std::unique_ptr<InputEventAck> response(new InputEventAck(
         input_event.type, ack_result, swap_latency_info,
@@ skipping 116 matching lines @@
   if (pending_input_event_ack_) {
     TRACE_EVENT_ASYNC_END0("input",
                            "RenderWidgetInputHandler::ThrottledInputEventAck",
                            pending_input_event_ack_.get());
     delegate_->OnInputEventAck(std::move(pending_input_event_ack_));
   }
   total_input_handling_time_this_frame_ = base::TimeDelta();
 }
 
 }  // namespace content