Plumb scroll elasticity layer from Blink to cc

Implement the 4-argument version of registerViewportLayers
for all implementers of WebLayerTreeView.

Add a scroll elasticity layer to cc::LayerTreeHost and through to
cc::LayerTreeHostImpl. These layers are still optional, and most
tests set them to NULL. Once the Blink side that pushes real layers
through is completed, the scroll elasticity layer will be required.

R=enne
TBR=jam
BUG=133097

Review URL: https://codereview.chromium.org/731863009

Cr-Commit-Position: refs/heads/master@{#305260}

2 files changed, 30 insertions, 3 deletions

diff --git a/mojo/services/html_viewer/weblayertreeview_impl.cc b/mojo/services/html_viewer/weblayertreeview_impl.cc
index 1f025a9..1251576 100644
--- a/mojo/services/html_viewer/weblayertreeview_impl.cc
+++ b/mojo/services/html_viewer/weblayertreeview_impl.cc
@@ -175,23 +175,44 @@ void WebLayerTreeViewImpl::registerForAnimations(blink::WebLayer* layer) {
 }
 
 void WebLayerTreeViewImpl::registerViewportLayers(
+    const blink::WebLayer* overscrollElasticityLayer,
     const blink::WebLayer* pageScaleLayer,
     const blink::WebLayer* innerViewportScrollLayer,
     const blink::WebLayer* outerViewportScrollLayer) {
   layer_tree_host_->RegisterViewportLayers(
+      static_cast<const cc_blink::WebLayerImpl*>(overscrollElasticityLayer)
+          ->layer(),
       static_cast<const cc_blink::WebLayerImpl*>(pageScaleLayer)->layer(),
       static_cast<const cc_blink::WebLayerImpl*>(innerViewportScrollLayer)
           ->layer(),
       // The outer viewport layer will only exist when using pinch virtual
       // viewports.
-      outerViewportScrollLayer ? static_cast<const cc_blink::WebLayerImpl*>(
-                                     outerViewportScrollLayer)->layer()
-                               : NULL);
+      outerViewportScrollLayer
+          ? static_cast<const cc_blink::WebLayerImpl*>(outerViewportScrollLayer)
+                ->layer()
+          : NULL);
+}
+
+void WebLayerTreeViewImpl::registerViewportLayers(
+    const blink::WebLayer* pageScaleLayer,
+    const blink::WebLayer* innerViewportScrollLayer,
+    const blink::WebLayer* outerViewportScrollLayer) {
+  layer_tree_host_->RegisterViewportLayers(
+      NULL, static_cast<const cc_blink::WebLayerImpl*>(pageScaleLayer)->layer(),
+      static_cast<const cc_blink::WebLayerImpl*>(innerViewportScrollLayer)
+          ->layer(),
+      // The outer viewport layer will only exist when using pinch virtual
+      // viewports.
+      outerViewportScrollLayer
+          ? static_cast<const cc_blink::WebLayerImpl*>(outerViewportScrollLayer)
+                ->layer()
+          : NULL);
 }
 
 void WebLayerTreeViewImpl::clearViewportLayers() {
   layer_tree_host_->RegisterViewportLayers(scoped_refptr<cc::Layer>(),
                                            scoped_refptr<cc::Layer>(),
+                                           scoped_refptr<cc::Layer>(),
                                            scoped_refptr<cc::Layer>());
 }
 
diff --git a/mojo/services/html_viewer/weblayertreeview_impl.h b/mojo/services/html_viewer/weblayertreeview_impl.h
index a567aaf..7ec38a9 100644
--- a/mojo/services/html_viewer/weblayertreeview_impl.h
+++ b/mojo/services/html_viewer/weblayertreeview_impl.h
@@ -96,6 +96,12 @@ class WebLayerTreeViewImpl : public blink::WebLayerTreeView,
   virtual void setDeferCommits(bool defer_commits) {}
   virtual void registerForAnimations(blink::WebLayer* layer) override;
   virtual void registerViewportLayers(
+      const blink::WebLayer* overscrollElasticityLayer,
+      const blink::WebLayer* pageScaleLayerLayer,
+      const blink::WebLayer* innerViewportScrollLayer,
+      const blink::WebLayer* outerViewportScrollLayer) override;
+  // TODO(ccameron): Remove this when Blink no longer calls it.
+  virtual void registerViewportLayers(
       const blink::WebLayer* page_scale_layer,
       const blink::WebLayer* inner_viewport_scroll_layer,
       const blink::WebLayer* outer_viewport_scroll_layer) override;