Introduce bottom controls to CC and let it respond to scrolling

content/common/resize_params.h

Index: content/common/resize_params.h
diff --git a/content/common/resize_params.h b/content/common/resize_params.h
index f9eb07c247df8f7ad499644a83864081efeb6ad6..bd6ac89817f1fbff19aa47af60a38964e52d83ef 100644
--- a/content/common/resize_params.h
+++ b/content/common/resize_params.h
@@ -34,6 +34,9 @@ struct CONTENT_EXPORT ResizeParams {
   // isn't supported).
   float top_controls_height;
 
+  // The height of the bottom controls.
+  float bottom_controls_height;
+
   // The size of the visible viewport, which may be smaller than the view if the
   // view is partially occluded (e.g. by a virtual keyboard).  The size is in
   // DPI-adjusted pixels.