Handle root layer fling Java-side in android_webview.

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 "base/basictypes.h"
 #include "base/json/json_writer.h"
@@ skipping 2099 matching lines @@
 }
 
 void LayerTreeHostImpl::ScrollEnd() {
   if (top_controls_manager_)
     top_controls_manager_->ScrollEnd();
   ClearCurrentlyScrollingLayer();
   StartScrollbarAnimation();
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::FlingScrollBegin() {
-  if (active_tree_->CurrentlyScrollingLayer())
-    return ScrollStarted;
+  if (!active_tree_->CurrentlyScrollingLayer())
+    return ScrollIgnored;
 
-  return ScrollIgnored;
+  if (settings_.ignore_root_layer_flings &&
+      active_tree_->CurrentlyScrollingLayer() ==
+          active_tree_->RootScrollLayer()) {
+    ClearCurrentlyScrollingLayer();
+    return ScrollIgnored;
+  }
+
+  return ScrollStarted;
 }
 
 void LayerTreeHostImpl::NotifyCurrentFlingVelocity(gfx::Vector2dF velocity) {
   current_fling_velocity_ = velocity;
 }
 
 void LayerTreeHostImpl::PinchGestureBegin() {
   pinch_gesture_active_ = true;
   previous_pinch_anchor_ = gfx::Point();
   client_->RenewTreePriority();
@@ skipping 356 matching lines @@
 
 ResourceProvider::ResourceId LayerTreeHostImpl::ResourceIdForUIResource(
     UIResourceId uid) const {
   UIResourceMap::const_iterator iter = ui_resource_map_.find(uid);
   if (iter != ui_resource_map_.end())
     return iter->second;
   return 0;
 }
 
 }  // namespace cc