Update from chromium https://crrev.com/301315

cc/trees/layer_tree_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_impl.h"
 
 #include <limits>
 #include <set>
 
 #include "base/debug/trace_event.h"
@@ skipping 33 matching lines @@
       : layer_(layer), delegate_(delegate), layer_tree_impl_(layer_tree) {}
   virtual ~LayerScrollOffsetDelegateProxy() {}
 
   gfx::ScrollOffset last_set_scroll_offset() const {
     return last_set_scroll_offset_;
   }
 
   // LayerScrollOffsetDelegate implementation.
   void SetTotalScrollOffset(const gfx::ScrollOffset& new_offset) override {
     last_set_scroll_offset_ = new_offset;
-    layer_tree_impl_->UpdateScrollOffsetDelegate();
   }
 
   gfx::ScrollOffset GetTotalScrollOffset() override {
     return layer_tree_impl_->GetDelegatedScrollOffset(layer_);
   }
 
   bool IsExternalFlingActive() const override {
     return delegate_->IsExternalFlingActive();
   }
 
+  void Update() const override {
+    layer_tree_impl_->UpdateScrollOffsetDelegate();
+  }
+
  private:
   LayerImpl* layer_;
   LayerScrollOffsetDelegate* delegate_;
   LayerTreeImpl* layer_tree_impl_;
   gfx::ScrollOffset last_set_scroll_offset_;
 };
 
 LayerTreeImpl::LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl)
     : layer_tree_host_impl_(layer_tree_host_impl),
       source_frame_number_(-1),
@@ skipping 848 matching lines @@
     }
 
     if (outer_viewport_scroll_layer_) {
       outer_viewport_scroll_delegate_proxy_ = make_scoped_ptr(
           new LayerScrollOffsetDelegateProxy(OuterViewportScrollLayer(),
                                              root_layer_scroll_offset_delegate_,
                                              this));
       outer_viewport_scroll_layer_->SetScrollOffsetDelegate(
           outer_viewport_scroll_delegate_proxy_.get());
     }
+
+    if (inner_viewport_scroll_layer_)
+      UpdateScrollOffsetDelegate();
   }
 }
 
 void LayerTreeImpl::OnRootLayerDelegatedScrollOffsetChanged() {
   DCHECK(root_layer_scroll_offset_delegate_);
   if (inner_viewport_scroll_layer_) {
     inner_viewport_scroll_layer_->DidScroll();
   }
   if (outer_viewport_scroll_layer_) {
     outer_viewport_scroll_layer_->DidScroll();
   }
 }
 
 void LayerTreeImpl::UpdateScrollOffsetDelegate() {
   DCHECK(InnerViewportScrollLayer());
+  DCHECK(!OuterViewportScrollLayer() || outer_viewport_scroll_delegate_proxy_);
   DCHECK(root_layer_scroll_offset_delegate_);
 
   gfx::ScrollOffset offset =
       inner_viewport_scroll_delegate_proxy_->last_set_scroll_offset();
 
   if (OuterViewportScrollLayer())
     offset += outer_viewport_scroll_delegate_proxy_->last_set_scroll_offset();
 
   root_layer_scroll_offset_delegate_->UpdateRootLayerState(
       offset,
@@ skipping 557 matching lines @@
                                   page_scale,
                                   duration.InSecondsF());
   }
 }
 
 scoped_ptr<PageScaleAnimation> LayerTreeImpl::TakePageScaleAnimation() {
   return page_scale_animation_.Pass();
 }
 
 }  // namespace cc