Revert of Cleanup viewport scrolling for future scroll customization work.

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"
@@ skipping 14 matching lines @@
   DCHECK(host_impl_);
 }
 
 void Viewport::Pan(const gfx::Vector2dF& delta) {
   gfx::Vector2dF pending_delta = delta;
   float page_scale = host_impl_->active_tree()->current_page_scale_factor();
   pending_delta.Scale(1 / page_scale);
   InnerScrollLayer()->ScrollBy(pending_delta);
 }
 
-gfx::Vector2dF Viewport::ScrollBy(const gfx::Vector2dF& delta,
-                                  const gfx::Point& viewport_point,
-                                  bool is_direct_manipulation,
-                                  bool affect_top_controls) {
-  gfx::Vector2dF pending_delta = delta;
-  if (affect_top_controls && ShouldTopControlsConsumeScroll(delta))
-    pending_delta -= ScrollTopControls(delta);
+Viewport::ScrollResult Viewport::ScrollBy(const gfx::Vector2dF& delta,
+                                          const gfx::Point& viewport_point,
+                                          bool is_wheel_scroll,
+                                          bool affect_top_controls) {
+  gfx::Vector2dF content_delta = delta;
+  ScrollResult result;
+
+  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_delta -=
-        host_impl_->ScrollLayer(OuterScrollLayer(), pending_delta,
-                                viewport_point, is_direct_manipulation);
+    pending_content_delta -= host_impl_->ScrollLayer(OuterScrollLayer(),
+                                                     pending_content_delta,
+                                                     viewport_point,
+                                                     is_wheel_scroll);
   }
 
   // TODO(bokan): This shouldn't be needed but removing it causes subtle
   // viewport movement during top controls manipulation.
-  if (gfx::ToRoundedVector2d(pending_delta).IsZero())
-    return delta;
+  if (!gfx::ToRoundedVector2d(pending_content_delta).IsZero()) {
+    pending_content_delta -= host_impl_->ScrollLayer(InnerScrollLayer(),
+                                                     pending_content_delta,
+                                                     viewport_point,
+                                                     is_wheel_scroll);
+    result.unused_scroll_delta = AdjustOverscroll(pending_content_delta);
+  }
 
-  pending_delta -=
-      host_impl_->ScrollLayer(InnerScrollLayer(), pending_delta, viewport_point,
-                              is_direct_manipulation);
-  pending_delta = AdjustOverscroll(pending_delta);
-  return delta - pending_delta;
+
+  result.applied_delta = content_delta - pending_content_delta;
+  return result;
 }
 
 void Viewport::SnapPinchAnchorIfWithinMargin(const gfx::Point& anchor) {
   gfx::SizeF viewport_size =
       host_impl_->active_tree()->InnerViewportContainerLayer()->bounds();
 
   if (anchor.x() < kPinchZoomSnapMarginDips)
     pinch_anchor_adjustment_.set_x(-anchor.x());
   else if (anchor.x() > viewport_size.width() - kPinchZoomSnapMarginDips)
     pinch_anchor_adjustment_.set_x(viewport_size.width() - anchor.x());
@@ skipping 118 matching lines @@
 
 LayerImpl* Viewport::InnerScrollLayer() const {
   return host_impl_->InnerViewportScrollLayer();
 }
 
 LayerImpl* Viewport::OuterScrollLayer() const {
   return host_impl_->OuterViewportScrollLayer();
 }
 
 }  // namespace cc