Roll Chrome into Mojo.

cc/blink/web_scrollbar_layer_impl.cc

 // Copyright 2014 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/blink/web_scrollbar_layer_impl.h"
 
 #include "cc/blink/scrollbar_impl.h"
 #include "cc/blink/web_layer_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/painted_scrollbar_layer.h"
@@ skipping 43 matching lines @@
 WebScrollbarLayerImpl::~WebScrollbarLayerImpl() {
 }
 
 blink::WebLayer* WebScrollbarLayerImpl::layer() {
   return layer_.get();
 }
 
 void WebScrollbarLayerImpl::setScrollLayer(blink::WebLayer* layer) {
   cc::Layer* scroll_layer =
       layer ? static_cast<WebLayerImpl*>(layer)->layer() : 0;
-  layer_->layer()->ToScrollbarLayer()->SetScrollLayer(scroll_layer->id());
+  layer_->layer()->ToScrollbarLayer()->SetScrollLayer(
+      scroll_layer ? scroll_layer->id() : cc::Layer::INVALID_ID);
 }
 
 void WebScrollbarLayerImpl::setClipLayer(blink::WebLayer* layer) {
   cc::Layer* clip_layer =
       layer ? static_cast<WebLayerImpl*>(layer)->layer() : 0;
-  layer_->layer()->ToScrollbarLayer()->SetClipLayer(clip_layer->id());
+  layer_->layer()->ToScrollbarLayer()->SetClipLayer(
+      clip_layer ? clip_layer->id() : cc::Layer::INVALID_ID);
 }
 
 }  // namespace cc_blink