Let LayerTreeHostImpl::ScrollAnimated scroll the outer viewport.

content/renderer/input/input_handler_proxy.cc

 // Copyright 2013 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 "content/renderer/input/input_handler_proxy.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 732 matching lines @@
                        "InputHandlerProxy::ExtendBoostedFlingTimeout",
                        TRACE_EVENT_SCOPE_THREAD);
   deferred_fling_cancel_time_seconds_ =
       event.timeStampSeconds + kFlingBoostTimeoutDelaySeconds;
   last_fling_boost_event_ = event;
 }
 
 void InputHandlerProxy::Animate(base::TimeTicks time) {
   // If using synchronous animate, then only expect Animate attempts started by
   // the synchronous system. Don't let the InputHandler try to Animate also.
-  DCHECK_IMPLIES(input_handler_->IsCurrentlyScrollingRoot(),
+  DCHECK_IMPLIES(input_handler_->IsCurrentlyScrollingInnerViewport(),
                  allow_root_animate_);
 
   if (scroll_elasticity_controller_)
     scroll_elasticity_controller_->Animate(time);
 
   if (!fling_curve_)
     return;
 
   last_fling_animate_time_ = time;
   double monotonic_time_sec = InSecondsF(time);
@@ skipping 161 matching lines @@
     }
   }
 
   return had_fling_animation;
 }
 
 void InputHandlerProxy::RequestAnimation() {
   // When a SynchronousInputHandler is present, root flings should go through
   // it to allow it to control when or if the root fling is animated. Non-root
   // flings always go through the normal InputHandler.
-  if (synchronous_input_handler_ && input_handler_->IsCurrentlyScrollingRoot())
+  if (synchronous_input_handler_ &&
+      input_handler_->IsCurrentlyScrollingInnerViewport())
     synchronous_input_handler_->SetNeedsSynchronousAnimateInput();
   else
     input_handler_->SetNeedsAnimateInput();
 }
 
 bool InputHandlerProxy::TouchpadFlingScroll(
     const WebFloatSize& increment) {
   WebMouseWheelEvent synthetic_wheel;
   synthetic_wheel.type = WebInputEvent::MouseWheel;
   synthetic_wheel.deltaX = increment.width;
@@ skipping 82 matching lines @@
   // trigger a scroll, e.g., with a trivial time delta between fling updates.
   // Return true in this case to prevent early fling termination.
   if (std::abs(clipped_increment.width) < kScrollEpsilon &&
       std::abs(clipped_increment.height) < kScrollEpsilon)
     return true;
 
   return did_scroll;
 }
 
 }  // namespace content