Fix bounds clamping during composited smooth scroll.

cc/animation/scroll_offset_animations_impl.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 "cc/animation/scroll_offset_animations_impl.h"
 
 #include "cc/animation/animation_events.h"
 #include "cc/animation/animation_host.h"
 #include "cc/animation/animation_id_provider.h"
 #include "cc/animation/animation_player.h"
@@ skipping 56 matching lines @@
 
   DCHECK_EQ(element_id, scroll_offset_animation_player_->element_id());
 
   Animation* animation =
       scroll_offset_animation_player_->element_animations()->GetAnimation(
           TargetProperty::SCROLL_OFFSET);
   if (!animation) {
     scroll_offset_animation_player_->DetachElement();
     return false;
   }
+  if (scroll_delta.IsZero())
+    return true;
 
   ScrollOffsetAnimationCurve* curve =
       animation->curve()->ToScrollOffsetAnimationCurve();
 
   gfx::ScrollOffset new_target =
       gfx::ScrollOffsetWithDelta(curve->target_value(), scroll_delta);
   new_target.SetToMax(gfx::ScrollOffset());
   new_target.SetToMin(max_scroll_offset);
 
   curve->UpdateTarget(
@@ skipping 22 matching lines @@
     ElementId element_id) {
   if (scroll_offset_animation_player_->element_id() != element_id) {
     if (scroll_offset_animation_player_->element_id())
       scroll_offset_animation_player_->DetachElement();
     if (element_id)
       scroll_offset_animation_player_->AttachElement(element_id);
   }
 }
 
 }  // namespace cc