Clean up viewport scrolling methods in CC

cc/layers/viewport.cc

Index: cc/layers/viewport.cc
diff --git a/cc/layers/viewport.cc b/cc/layers/viewport.cc
index f2f6282d166a4bee64c6952afbaed0b690689e9d..8b58c5f3345c0b209d1d5cee67229884c41422cf 100644
--- a/cc/layers/viewport.cc
+++ b/cc/layers/viewport.cc
@@ -68,6 +68,14 @@ Viewport::ScrollResult Viewport::ScrollBy(const gfx::Vector2dF& delta,
   return result;
 }
 
+void Viewport::ScrollByInnerFirst(const gfx::Vector2dF& delta) {
+  LayerImpl* scroll_layer = InnerScrollLayer();
+
+  gfx::Vector2dF unused_delta = scroll_layer->ScrollBy(delta);
+  if (!unused_delta.IsZero() && OuterScrollLayer())
+    OuterScrollLayer()->ScrollBy(unused_delta);
+}
+
 bool Viewport::ShouldAnimateViewport(const gfx::Vector2dF& viewport_delta,
                                      const gfx::Vector2dF& pending_delta) {
   float max_dim_viewport_delta =
@@ -186,6 +194,10 @@ void Viewport::PinchEnd() {
   pinch_zoom_active_ = false;
 }
 
+LayerImpl* Viewport::MainScrollLayer() const {
+  return InnerScrollLayer();
+}
+
 gfx::Vector2dF Viewport::ScrollTopControls(const gfx::Vector2dF& delta) {
   gfx::Vector2dF excess_delta =
       host_impl_->top_controls_manager()->ScrollBy(delta);