Introduce bottom controls to CC and let it respond to scrolling

cc/trees/layer_tree_impl.h

 // Copyright 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.
 
 #ifndef CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 400 matching lines @@
   bool top_controls_shrink_blink_size() const {
     return top_controls_shrink_blink_size_;
   }
   bool SetCurrentTopControlsShownRatio(float ratio);
   float CurrentTopControlsShownRatio() const {
     return top_controls_shown_ratio_->Current(IsActiveTree());
   }
   void set_top_controls_height(float top_controls_height);
   float top_controls_height() const { return top_controls_height_; }
   void PushTopControlsFromMainThread(float top_controls_shown_ratio);
+  void set_bottom_controls_height(float bottom_controls_height);
+  float bottom_controls_height() const { return bottom_controls_height_; }
 
   void SetPendingPageScaleAnimation(
       std::unique_ptr<PendingPageScaleAnimation> pending_animation);
   std::unique_ptr<PendingPageScaleAnimation> TakePendingPageScaleAnimation();
 
   void DidUpdateScrollOffset(int layer_id, int transform_id);
   void DidUpdateScrollState(int layer_id);
 
   bool IsAnimatingFilterProperty(const LayerImpl* layer) const;
   bool IsAnimatingOpacityProperty(const LayerImpl* layer) const;
@@ skipping 141 matching lines @@
   UIResourceRequestQueue ui_resource_request_queue_;
 
   bool have_scroll_event_handlers_;
   EventListenerProperties event_listener_properties_[static_cast<size_t>(
       EventListenerClass::kNumClasses)];
 
   // Whether or not Blink's viewport size was shrunk by the height of the top
   // controls at the time of the last layout.
   bool top_controls_shrink_blink_size_;
   float top_controls_height_;
+  float bottom_controls_height_;
 
   // The amount that the top controls are shown from 0 (hidden) to 1 (fully
   // shown).
   scoped_refptr<SyncedTopControls> top_controls_shown_ratio_;
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_