Allow WebExternalTextureLayers to receive a bitmap along with a mailbox

cc/layers/texture_layer.cc

Index: cc/layers/texture_layer.cc
diff --git a/cc/layers/texture_layer.cc b/cc/layers/texture_layer.cc
index a6022dd2408faf496db47913187e4d4864f0bf70..87e233fb5f12efb52ab30ea9cf2af14f97a34564 100644
--- a/cc/layers/texture_layer.cc
+++ b/cc/layers/texture_layer.cc
@@ -159,6 +159,10 @@ void TextureLayer::WillModifyTexture() {
   }
 }
 
+bool TextureLayer::MustUseBitmap() {
+  return layer_tree_host()->UsingSoftwareRenderer();
+}
+
 void TextureLayer::SetNeedsDisplayRect(const gfx::RectF& dirty_rect) {
   Layer::SetNeedsDisplayRect(dirty_rect);