Introduce bottom controls to CC and let it respond to scrolling

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 <stddef.h>
 
 #include <bitset>
@@ skipping 188 matching lines @@
       InputHandler::ScrollInputType type) const override;
   EventListenerProperties GetEventListenerProperties(
       EventListenerClass event_class) const override;
   bool DoTouchEventsBlockScrollAt(const gfx::Point& viewport_port) override;
   std::unique_ptr<SwapPromiseMonitor> CreateLatencyInfoSwapPromiseMonitor(
       ui::LatencyInfo* latency) override;
   ScrollElasticityHelper* CreateScrollElasticityHelper() override;
 
   // TopControlsManagerClient implementation.
   float TopControlsHeight() const override;
+  float BottomControlsHeight() const override;
   void SetCurrentTopControlsShownRatio(float offset) override;
   float CurrentTopControlsShownRatio() const override;
   void DidChangeTopControlsPosition() override;
   bool HaveRootScrollLayer() const override;
 
   void UpdateViewportContainerSizes();
 
   void set_resourceless_software_draw_for_testing() {
     resourceless_software_draw_ = true;
   }
@@ skipping 632 matching lines @@
 
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_