Don't block the browser on FlingCancel acks.

content/browser/renderer_host/render_widget_host_impl.cc

 // Copyright (c) 2012 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/render_widget_host_impl.h"
 
 #include <utility>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 806 matching lines @@
   ForwardInputEvent(wheel_event, sizeof(WebMouseWheelEvent), false);
 }
 
 void RenderWidgetHostImpl::ForwardGestureEvent(
     const WebKit::WebGestureEvent& gesture_event) {
   TRACE_EVENT0("renderer_host", "RenderWidgetHostImpl::ForwardGestureEvent");
   if (ignore_input_events_ || process_->IgnoreInputEvents())
     return;
 
   if (gesture_event_pending_) {
-   if (coalesced_gesture_events_.empty() ||
-       !ShouldCoalesceGestureEvents(coalesced_gesture_events_.back(),
+    if (coalesced_gesture_events_.empty() ||
+        !ShouldCoalesceGestureEvents(coalesced_gesture_events_.back(),
                                     gesture_event)) {
-     coalesced_gesture_events_.push_back(gesture_event);
+      coalesced_gesture_events_.push_back(gesture_event);
     } else {
       WebGestureEvent* last_gesture_event =
           &coalesced_gesture_events_.back();
       last_gesture_event->deltaX += gesture_event.deltaX;
       last_gesture_event->deltaY += gesture_event.deltaY;
       DCHECK_GE(gesture_event.timeStampSeconds,
                 last_gesture_event->timeStampSeconds);
       last_gesture_event->timeStampSeconds = gesture_event.timeStampSeconds;
     }
     return;
   }
-  gesture_event_pending_ = true;
 
-  if (gesture_event.type == WebInputEvent::GestureFlingCancel)
+  if (gesture_event.type == WebInputEvent::GestureFlingCancel) {
+    // We don't throttle FlingCancel, because it usually goes right through to
+    // the WebKit thread and blocking on WebKit is bad.
     tap_suppression_controller_->GestureFlingCancel(
         gesture_event.timeStampSeconds);
+  } else {
+    gesture_event_pending_ = true;
+  }
+
   ForwardInputEvent(gesture_event, sizeof(WebGestureEvent), false);
 }
 
 void RenderWidgetHostImpl::ForwardKeyboardEvent(
     const NativeWebKeyboardEvent& key_event) {
   TRACE_EVENT0("renderer_host", "RenderWidgetHostImpl::ForwardKeyboardEvent");
   if (ignore_input_events_ || process_->IgnoreInputEvents())
     return;
 
   if (key_event.type == WebKeyboardEvent::Char &&
@@ skipping 625 matching lines @@
         coalesced_mouse_wheel_events_.front();
     coalesced_mouse_wheel_events_.pop_front();
     ForwardWheelEvent(next_wheel_event);
   }
 
   if (!processed && !is_hidden_ && view_)
     view_->UnhandledWheelEvent(current_wheel_event_);
 }
 
 void RenderWidgetHostImpl::ProcessGestureAck(bool processed, int type) {
-  if (type == WebInputEvent::GestureFlingCancel)
+  if (type == WebInputEvent::GestureFlingCancel) {
     tap_suppression_controller_->GestureFlingCancelAck(processed);
+  } else {
+    gesture_event_pending_ = false;
 
-  gesture_event_pending_ = false;
-
-  // Now send the next (coalesced) gesture event.
-  if (!coalesced_gesture_events_.empty()) {
-    WebGestureEvent next_gesture_event =
-        coalesced_gesture_events_.front();
-    coalesced_gesture_events_.pop_front();
-    ForwardGestureEvent(next_gesture_event);
+    // Now flush out the queued events until we hit one that needs another ack.
+    while (!gesture_event_pending_ && !coalesced_gesture_events_.empty()) {
+      WebGestureEvent next_gesture_event =
+          coalesced_gesture_events_.front();
+      coalesced_gesture_events_.pop_front();
+      ForwardGestureEvent(next_gesture_event);
+    }
   }
 }
 
 void RenderWidgetHostImpl::ProcessTouchAck(
     WebInputEvent::Type type, bool processed) {
   if (view_)
     view_->ProcessTouchAck(type, processed);
 }
 
 void RenderWidgetHostImpl::OnMsgFocus() {
@@ skipping 360 matching lines @@
   // indicate that no callback is in progress (i.e. without this line
   // DelayedAutoResized will not get called again).
   new_auto_size_.SetSize(0, 0);
   if (!should_auto_resize_)
     return;
 
   OnRenderAutoResized(new_size);
 }
 
 }  // namespace content