Roll Chrome into Mojo.

cc/blink/web_scrollbar_layer_impl.cc

Index: cc/blink/web_scrollbar_layer_impl.cc
diff --git a/cc/blink/web_scrollbar_layer_impl.cc b/cc/blink/web_scrollbar_layer_impl.cc
index dcc8d6fee1501a743efd03fba6bb6c1e699cec55..c94f2c5a9cc3a26500d9bb73ab0063d9e3d3ff37 100644
--- a/cc/blink/web_scrollbar_layer_impl.cc
+++ b/cc/blink/web_scrollbar_layer_impl.cc
@@ -61,13 +61,15 @@ blink::WebLayer* WebScrollbarLayerImpl::layer() {
 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