Clean up viewport scrolling methods in CC

cc/layers/viewport.h

 // 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.
 
 #ifndef CC_LAYERS_VIEWPORT_H_
 #define CC_LAYERS_VIEWPORT_H_
 
 #include <memory>
 
 #include "base/gtest_prod_util.h"
@@ skipping 30 matching lines @@
   // affecting the top controls or outer viewport.
   void Pan(const gfx::Vector2dF& delta);
 
   // Scrolls the viewport, applying the unique bubbling between the inner and
   // outer viewport. Scrolls can be consumed by top controls.
   ScrollResult ScrollBy(const gfx::Vector2dF& delta,
                         const gfx::Point& viewport_point,
                         bool is_wheel_scroll,
                         bool affect_top_controls);
 
+  // Scrolls the viewport. Unlike the above method, scrolls the inner before
+  // the outer viewport. Doesn't affect top controls or return a result since
+  // callers don't need it.
+  void ScrollByInnerFirst(const gfx::Vector2dF& delta);
+
   // Scrolls the viewport, bubbling the delta between the inner and outer
   // viewport. Only animates either of the two viewports.
   gfx::Vector2dF ScrollAnimated(const gfx::Vector2dF& delta,
                                 base::TimeDelta delayed_by);
 
   void PinchUpdate(float magnify_delta, const gfx::Point& anchor);
   void PinchEnd();
 
+  // Returns the "representative" viewport layer. That is, the one that's set
+  // as the currently scrolling layer when the viewport scrolls and the one used
+  // in the scrolling code to indicate scrolling should happen via this class.
+  LayerImpl* MainScrollLayer() const;
+
  private:
   explicit Viewport(LayerTreeHostImpl* host_impl);
 
   // Returns true if viewport_delta is stricly less than pending_delta.
   static bool ShouldAnimateViewport(const gfx::Vector2dF& viewport_delta,
                                     const gfx::Vector2dF& pending_delta);
   bool ShouldTopControlsConsumeScroll(const gfx::Vector2dF& scroll_delta) const;
   gfx::Vector2dF AdjustOverscroll(const gfx::Vector2dF& delta) const;
 
   // Sends the delta to the top controls, returns the amount applied.
@@ skipping 16 matching lines @@
   gfx::Vector2d pinch_anchor_adjustment_;
 
   FRIEND_TEST_ALL_PREFIXES(ViewportTest, ShouldAnimateViewport);
 
   DISALLOW_COPY_AND_ASSIGN(Viewport);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_VIEWPORT_H_