Defer synthetic gesture completions until events have been flushed

content/browser/renderer_host/input/synthetic_gesture_controller.cc

 // Copyright 2013 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/browser/renderer_host/input/synthetic_gesture_controller.h"
 
 #include "base/debug/trace_event.h"
 #include "content/browser/renderer_host/input/synthetic_gesture_target.h"
 #include "content/common/input/synthetic_smooth_scroll_gesture_params.h"
 #include "content/common/input_messages.h"
@@ skipping 18 matching lines @@
 
   if (was_empty)
     StartGesture(*pending_gesture_queue_.FrontGesture());
 }
 
 void SyntheticGestureController::Flush(base::TimeTicks timestamp) {
   TRACE_EVENT0("input", "SyntheticGestureController::Flush");
   if (pending_gesture_queue_.IsEmpty())
     return;
 
+  if (pending_gesture_result_)
+    return;
+
   SyntheticGesture* gesture = pending_gesture_queue_.FrontGesture();
-  SyntheticGesture::Result result = gesture->ForwardInputEvents(timestamp,
-      gesture_target_.get());
+  SyntheticGesture::Result result =
+      gesture->ForwardInputEvents(timestamp, gesture_target_.get());
 
   if (result == SyntheticGesture::GESTURE_RUNNING) {
     gesture_target_->SetNeedsFlush();
     return;
   }
 
-  StopGesture(*gesture, pending_gesture_queue_.FrontCallback(), result);
+  // It's possible that all events generated by the gesture have been fully
+  // dispatched at this point, in which case |OnDidFlushInput()| was called
+  // before |pending_gesture_result_| was initialized. Requesting another flush
+  // will trigger the necessary gesture-ending call to |OnDidFlushInput()|.
+  pending_gesture_result_.reset(new SyntheticGesture::Result(result));
+  gesture_target_->SetNeedsFlush();
+}
+
+void SyntheticGestureController::OnDidFlushInput() {
+  if (!pending_gesture_result_)
+    return;
+
+  DCHECK(!pending_gesture_queue_.IsEmpty());
+  StopGesture(*pending_gesture_queue_.FrontGesture(),
+              pending_gesture_queue_.FrontCallback(),
+              *pending_gesture_result_.Pass());
   pending_gesture_queue_.Pop();
 
   if (!pending_gesture_queue_.IsEmpty())
     StartGesture(*pending_gesture_queue_.FrontGesture());
 }
 
 void SyntheticGestureController::StartGesture(const SyntheticGesture& gesture) {
   TRACE_EVENT_ASYNC_BEGIN0("input,benchmark",
                            "SyntheticGestureController::running",
                            &gesture);
@@ skipping 13 matching lines @@
 }
 
 SyntheticGestureController::GestureAndCallbackQueue::GestureAndCallbackQueue() {
 }
 
 SyntheticGestureController::GestureAndCallbackQueue::
     ~GestureAndCallbackQueue() {
 }
 
 }  // namespace content