Let LayerTreeHostImpl::ScrollAnimated scroll the outer viewport.

cc/layers/layer_impl.cc

 // Copyright 2012 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/layer_impl.h"
 
 #include "base/json/json_reader.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 508 matching lines @@
       return InputHandler::SCROLL_ON_MAIN_THREAD;
     }
   }
 
   if (have_scroll_event_handlers() &&
       effective_block_mode & SCROLL_BLOCKS_ON_SCROLL_EVENT) {
     TRACE_EVENT0("cc", "LayerImpl::tryScroll: Failed ScrollEventHandlers");
     return InputHandler::SCROLL_ON_MAIN_THREAD;
   }
 
-  if (type == InputHandler::WHEEL && have_wheel_event_handlers() &&
+  if ((type == InputHandler::WHEEL || type == InputHandler::ANIMATED_WHEEL) &&
+      have_wheel_event_handlers() &&
       effective_block_mode & SCROLL_BLOCKS_ON_WHEEL_EVENT) {
     TRACE_EVENT0("cc", "LayerImpl::tryScroll: Failed WheelEventHandlers");
     return InputHandler::SCROLL_ON_MAIN_THREAD;
   }
 
   if (!scrollable()) {
     TRACE_EVENT0("cc", "LayerImpl::tryScroll: Ignored not scrollable");
     return InputHandler::SCROLL_IGNORED;
   }
 
@@ skipping 1257 matching lines @@
   }
 
   // TODO(enne): the transform needs to come from property trees instead of
   // draw properties.
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       draw_properties().target_space_transform, default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc