Introduce bottom controls to CC and let it respond to scrolling

cc/input/top_controls_manager.cc

Index: cc/input/top_controls_manager.cc
diff --git a/cc/input/top_controls_manager.cc b/cc/input/top_controls_manager.cc
index 2b7b55b3c5de69a840d52f84b2fa3029d27565a8..5f23e9a5f76f621a67f172d35a32ceaf87ec36c7 100644
--- a/cc/input/top_controls_manager.cc
+++ b/cc/input/top_controls_manager.cc
@@ -68,6 +68,18 @@ float TopControlsManager::TopControlsHeight() const {
   return client_->TopControlsHeight();
 }
 
+float TopControlsManager::BottomControlsHeight() const {
+  return client_->BottomControlsHeight();
+}
+
+float TopControlsManager::ControlsBottomOffset() const {
+  return BottomControlsHeight() - ContentBottomOffset();
+}
+
+float TopControlsManager::ContentBottomOffset() const {
+  return TopControlsShownRatio() * BottomControlsHeight();
+}
+
 void TopControlsManager::UpdateTopControlsState(TopControlsState constraints,
                                                 TopControlsState current,
                                                 bool animate) {