Allow WebExternalTextureLayers to receive a bitmap along with a mailbox

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 8d93426f32ea842a2d7d437efc3905d12adae566..54f61beaaa641cbc9962f46fdaa075b4859fd6e0 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -52,7 +52,8 @@ RendererCapabilities::RendererCapabilities()
       using_offscreen_context3d(false),
       max_texture_size(0),
       avoid_pow2_textures(false),
-      using_map_image(false) {}
+      using_map_image(false),
+      using_shared_memory_resources(false) {}
 
 RendererCapabilities::~RendererCapabilities() {}
 
@@ -682,6 +683,10 @@ void LayerTreeHost::CalculateLCDTextMetricsCallback(Layer* layer) {
   }
 }
 
+bool LayerTreeHost::UsingSharedMemoryResources() {
+  return GetRendererCapabilities().using_shared_memory_resources;
+}
+
 void LayerTreeHost::UpdateLayers(Layer* root_layer,
                                  ResourceUpdateQueue* queue) {
   TRACE_EVENT1("cc", "LayerTreeHost::UpdateLayers",