Made fling gestures always bubble between inner and outer viewports.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 2222 matching lines @@
       applied_delta = ScrollLayerWithLocalDelta(layer_impl, pending_delta);
     }
 
     // If the layer wasn't able to move, try the next one in the hierarchy.
     float move_threshold = 0.1f;
     bool did_move_layer_x = std::abs(applied_delta.x()) > move_threshold;
     bool did_move_layer_y = std::abs(applied_delta.y()) > move_threshold;
     did_scroll_x |= did_move_layer_x;
     did_scroll_y |= did_move_layer_y;
     if (!did_move_layer_x && !did_move_layer_y) {
-      if (should_bubble_scrolls_ || !did_lock_scrolling_layer_)
+      // Scrolls should always bubble between the outer and inner viewports
+      if (should_bubble_scrolls_ || !did_lock_scrolling_layer_ ||
+          layer_impl == OuterViewportScrollLayer())
         continue;
       else
         break;
     }
 
     if (layer_impl == InnerViewportScrollLayer())
       unused_root_delta.Subtract(applied_delta);
 
     did_lock_scrolling_layer_ = true;
     if (!should_bubble_scrolls_) {
@@ skipping 746 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc