Added experiment for changing viewport scroll ordering.

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 "cc/input/top_controls_manager.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gfx/geometry/vector2d_conversions.h"
 #include "ui/gfx/geometry/vector2d_f.h"
 
 namespace cc {
 
 // static
 scoped_ptr<Viewport> Viewport::Create(
     LayerTreeHostImpl* host_impl) {
   return make_scoped_ptr(new Viewport(host_impl));
 }
 
 Viewport::Viewport(LayerTreeHostImpl* host_impl)
     : host_impl_(host_impl) {
   DCHECK(host_impl_);
 }
 
+void Viewport::Pan(const gfx::Vector2dF& delta) {
+  gfx::Vector2dF pending_delta = delta;
+
+  pending_delta -= host_impl_->ScrollLayer(InnerScrollLayer(),
+                                           pending_delta,
+                                           gfx::Point(),
+                                           false);
+}
+
 Viewport::ScrollResult Viewport::ScrollBy(const gfx::Vector2dF& delta,
                                           const gfx::Point& viewport_point,
-                                          bool is_wheel_scroll) {
+                                          bool is_wheel_scroll,
+                                          bool affect_top_controls) {
   gfx::Vector2dF content_delta = delta;
   ScrollResult result;
 
-  if (ShouldTopControlsConsumeScroll(delta)) {
+  if (affect_top_controls && ShouldTopControlsConsumeScroll(delta)) {
     result.top_controls_applied_delta = ScrollTopControls(delta);
     content_delta -= result.top_controls_applied_delta;
   }
 
   gfx::Vector2dF pending_content_delta = content_delta;
 
   if (OuterScrollLayer()) {
     pending_content_delta -= host_impl_->ScrollLayer(OuterScrollLayer(),
                                                      pending_content_delta,
                                                      viewport_point,
@@ skipping 80 matching lines @@
 
 LayerImpl* Viewport::InnerScrollLayer() const {
   return host_impl_->InnerViewportScrollLayer();
 }
 
 LayerImpl* Viewport::OuterScrollLayer() const {
   return host_impl_->OuterViewportScrollLayer();
 }
 
 }  // namespace cc