Don't block the browser on FlingCancel acks.

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 33652c937ee5c1599bab26bc3c4dec61772b7265..3556a19fa95099c191f42f1fedb61658f3191751 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -824,10 +824,10 @@ void RenderWidgetHostImpl::ForwardGestureEvent(
     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();
@@ -839,11 +839,16 @@ void RenderWidgetHostImpl::ForwardGestureEvent(
     }
     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);
 }
 
@@ -1489,17 +1494,18 @@ void RenderWidgetHostImpl::ProcessWheelAck(bool processed) {
 }
 
 void RenderWidgetHostImpl::ProcessGestureAck(bool processed, int type) {
-  if (type == WebInputEvent::GestureFlingCancel)
+  if (type == WebInputEvent::GestureFlingCancel) {
     tap_suppression_controller_->GestureFlingCancelAck(processed);
-
-  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);
+  } else {
+    gesture_event_pending_ = false;
+
+    // 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);
+    }
   }
 }