Made double-tap zoom work in pinch virtual viewport mode (Chromium-side).

cc/trees/layer_tree_host_impl.h

 // 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 504 matching lines @@
   void CreateAndSetRenderer();
   void CreateAndSetTileManager();
   void DestroyTileManager();
   void ReleaseTreeResources();
   void EnforceZeroBudget(bool zero_budget);
 
   bool UsePendingTreeForSync() const;
   bool UseZeroCopyRasterizer() const;
   bool UseOneCopyRasterizer() const;
 
+  // Scroll by preferring to move the outer viewport first, only moving the
+  // inner if the outer is at its scroll extents.
   void ScrollViewportBy(gfx::Vector2dF scroll_delta);
+  // Scroll by preferring to move the inner viewport first, only moving the
+  // outer if the inner is at its scroll extents.
+  void ScrollViewportInnerFirst(gfx::Vector2dF scroll_delta);
   void AnimatePageScale(base::TimeTicks monotonic_time);
   void AnimateScrollbars(base::TimeTicks monotonic_time);
   void AnimateTopControls(base::TimeTicks monotonic_time);
 
   gfx::Vector2dF ScrollLayerWithViewportSpaceDelta(
       LayerImpl* layer_impl,
       float scale_from_viewport_to_screen_space,
       const gfx::PointF& viewport_point,
       const gfx::Vector2dF& viewport_delta);
 
@@ skipping 166 matching lines @@
 
   std::vector<PictureLayerImpl*> picture_layers_;
   std::vector<PictureLayerImpl::Pair> picture_layer_pairs_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_