Cleanup viewport scrolling for future scroll customization work.

cc/layers/viewport.cc

Index: cc/layers/viewport.cc
diff --git a/cc/layers/viewport.cc b/cc/layers/viewport.cc
index 059e0a491a9f5bbc20a12448edf69d274d7b566c..1039a1e7d9c85df7330f56338e9a5e91942079fe 100644
--- a/cc/layers/viewport.cc
+++ b/cc/layers/viewport.cc
@@ -32,40 +32,30 @@ void Viewport::Pan(const gfx::Vector2dF& delta) {
   InnerScrollLayer()->ScrollBy(pending_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;
+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);
 
   if (OuterScrollLayer()) {
-    pending_content_delta -= host_impl_->ScrollLayer(OuterScrollLayer(),
-                                                     pending_content_delta,
-                                                     viewport_point,
-                                                     is_wheel_scroll);
+    pending_delta -=
+        host_impl_->ScrollLayer(OuterScrollLayer(), pending_delta,
+                                viewport_point, is_direct_manipulation);
   }
 
   // TODO(bokan): This shouldn't be needed but removing it causes subtle
   // viewport movement during top controls manipulation.
-  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);
-  }
-
-
-  result.applied_delta = content_delta - pending_content_delta;
-  return result;
+  if (gfx::ToRoundedVector2d(pending_delta).IsZero())
+    return delta;
+
+  pending_delta -=
+      host_impl_->ScrollLayer(InnerScrollLayer(), pending_delta, viewport_point,
+                              is_direct_manipulation);
+  pending_delta = AdjustOverscroll(pending_delta);
+  return delta - pending_delta;
 }
 
 void Viewport::SnapPinchAnchorIfWithinMargin(const gfx::Point& anchor) {