Introduce bottom controls to CC and let it respond to scrolling

cc/ipc/compositor_frame_metadata_struct_traits.h

Index: cc/ipc/compositor_frame_metadata_struct_traits.h
diff --git a/cc/ipc/compositor_frame_metadata_struct_traits.h b/cc/ipc/compositor_frame_metadata_struct_traits.h
index fedd13ef8673eac64743e0cacb18b4b27443c53b..861335f584725c58fd10684829d14405eeaaabfe 100644
--- a/cc/ipc/compositor_frame_metadata_struct_traits.h
+++ b/cc/ipc/compositor_frame_metadata_struct_traits.h
@@ -57,14 +57,24 @@ struct StructTraits<cc::mojom::CompositorFrameMetadata,
     return metadata.root_overflow_y_hidden;
   }
 
-  static gfx::Vector2dF location_bar_offset(
+  static gfx::Vector2dF top_controls_height(
       const cc::CompositorFrameMetadata& metadata) {
-    return metadata.location_bar_offset;
+    return metadata.top_controls_height;
   }
 
-  static gfx::Vector2dF location_bar_content_translation(
+  static float top_controls_shown_ratio(
       const cc::CompositorFrameMetadata& metadata) {
-    return metadata.location_bar_content_translation;
+    return metadata.top_controls_shown_ratio;
+  }
+
+  static gfx::Vector2dF bottom_controls_height(
+      const cc::CompositorFrameMetadata& metadata) {
+    return metadata.bottom_controls_height;
+  }
+
+  static float bottom_controls_shown_ratio(
+      const cc::CompositorFrameMetadata& metadata) {
+    return metadata.bottom_controls_shown_ratio;
   }
 
   static uint32_t root_background_color(