Introduce bottom controls to CC and let it respond to scrolling

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 7651d0305dec6d919874fa6380b0de1110007eaf..8d562ae31244835270086051e53f555c3a28e71b 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -519,6 +519,7 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
   sync_tree->set_top_controls_shrink_blink_size(
       top_controls_shrink_blink_size_);
   sync_tree->set_top_controls_height(top_controls_height_);
+  sync_tree->set_bottom_controls_height(bottom_controls_height_);
   sync_tree->PushTopControlsFromMainThread(top_controls_shown_ratio_);
 
   host_impl->SetHasGpuRasterizationTrigger(has_gpu_rasterization_trigger_);
@@ -834,6 +835,14 @@ void LayerTreeHost::SetTopControlsShownRatio(float ratio) {
   SetNeedsCommit();
 }
 
+void LayerTreeHost::setBottomControlHeight(float height) {
+  if (bottom_controls_height_ == height)
+    return;
+
+  bottom_controls_height_ = height;
+  SetNeedsCommit();
+}
+
 void LayerTreeHost::ApplyPageScaleDeltaFromImplSide(float page_scale_delta) {
   DCHECK(CommitRequested());
   if (page_scale_delta == 1.f)