Only emit a fallback SurfaceDrawQuad if differs from primary

cc/layers/surface_layer_impl.cc

Index: cc/layers/surface_layer_impl.cc
diff --git a/cc/layers/surface_layer_impl.cc b/cc/layers/surface_layer_impl.cc
index 16eac7bfbefeabd8e451c67e06dbfe6d920d8f29..17f78a3570514080b7c852a82555a857f9f2e11f 100644
--- a/cc/layers/surface_layer_impl.cc
+++ b/cc/layers/surface_layer_impl.cc
@@ -66,7 +66,9 @@ void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
   AppendRainbowDebugBorder(render_pass);
   auto* primary = CreateSurfaceDrawQuad(
       render_pass, SurfaceDrawQuadType::PRIMARY, primary_surface_info_);
-  if (primary) {
+  // Emitting a fallback SurfaceDrawQuad is unnecessary if the primary and
+  // fallback surface Ids match.
+  if (primary && fallback_surface_info_.id() != primary_surface_info_.id()) {

[vmpstr, 2017/02/16 00:52:12]

I'm guessing this comparison takes into account that fallback_surface_info_.id()
may not be valid

[Fady Samuel, 2017/02/16 01:16:10]

If the fallback SurfaceId is invalid  then CreateSurfaceDrawQuad will exit
early.

     primary->fallback_quad = CreateSurfaceDrawQuad(
         render_pass, SurfaceDrawQuadType::FALLBACK, fallback_surface_info_);
   }