cc: Add a rails argument to InputHandler::ScrollBy

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 
@@ skipping 2575 matching lines @@
                                      scale_factor);
   }
 
   return ScrollLayerWithViewportSpaceDelta(layer_impl,
                                            viewport_point,
                                            delta);
 }
 
 InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
     const gfx::Point& viewport_point,
-    const gfx::Vector2dF& scroll_delta) {
+    const gfx::Vector2dF& unrailed_scroll_delta,
+    InputHandler::RailsMode rails_mode) {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBy");
   if (!CurrentlyScrollingLayer())
     return InputHandlerScrollResult();
 
-  gfx::Vector2dF pending_delta = scroll_delta;
+  gfx::Vector2dF pending_delta = unrailed_scroll_delta;
+  if (rails_mode == InputHandler::RAILS_MODE_HORIZONTAL)
+    pending_delta.set_y(0);
+  if (rails_mode == InputHandler::RAILS_MODE_VERTICAL)
+    pending_delta.set_x(0);
   gfx::Vector2dF unused_root_delta;
   bool did_scroll_x = false;
   bool did_scroll_y = false;
   bool did_scroll_top_controls = false;
 
   for (LayerImpl* layer_impl = CurrentlyScrollingLayer();
        layer_impl;
        layer_impl = layer_impl->parent()) {
     // Skip the outer viewport scroll layer so that we try to scroll the
     // viewport only once. i.e. The inner viewport layer represents the
@@ skipping 804 matching lines @@
   new_target.SetToMin(layer_impl->MaxScrollOffset());
 
   curve->UpdateTarget(
       animation->TrimTimeToCurrentIteration(CurrentBeginFrameArgs().frame_time)
           .InSecondsF(),
       new_target);
 
   return true;
 }
 }  // namespace cc