Clean up viewport scrolling methods in CC

cc/layers/viewport.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/viewport.h"
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/trees/layer_tree_host_impl.h"
@@ skipping 50 matching lines @@
       scroll_tree.Node(OuterScrollLayer()->scroll_tree_index());
   pending_content_delta -= host_impl_->ScrollSingleNode(
       outer_node, pending_content_delta, viewport_point, is_direct_manipulation,
       &scroll_tree);
   result.consumed_delta = delta - AdjustOverscroll(pending_content_delta);
 
   result.content_scrolled_delta = content_delta - pending_content_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 =
       std::max(std::abs(viewport_delta.x()), std::abs(viewport_delta.y()));
   float max_dim_pending_delta =
       std::max(std::abs(pending_delta.x()), std::abs(pending_delta.y()));
   return max_dim_viewport_delta > max_dim_pending_delta;
 }
 
 gfx::Vector2dF Viewport::ScrollAnimated(const gfx::Vector2dF& delta,
@@ skipping 98 matching lines @@
   move -= InnerScrollLayer()->ClampScrollToMaxScrollOffset();
 
   Pan(move);
 }
 
 void Viewport::PinchEnd() {
   pinch_anchor_adjustment_ = gfx::Vector2d();
   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);
 
   return delta - excess_delta;
 }
 
 bool Viewport::ShouldTopControlsConsumeScroll(
     const gfx::Vector2dF& scroll_delta) const {
   // Always consume if it's in the direction to show the top controls.
@@ skipping 44 matching lines @@
 
 LayerImpl* Viewport::InnerScrollLayer() const {
   return host_impl_->InnerViewportScrollLayer();
 }
 
 LayerImpl* Viewport::OuterScrollLayer() const {
   return host_impl_->OuterViewportScrollLayer();
 }
 
 }  // namespace cc