Mac Overlays: Add sandwich strategy

cc/output/output_surface.cc

Index: cc/output/output_surface.cc
diff --git a/cc/output/output_surface.cc b/cc/output/output_surface.cc
index 0786d660d4a58a3e24c03dabc3411f9d3e08cd9a..056879f49d84ba444142101690da109437208d14 100644
--- a/cc/output/output_surface.cc
+++ b/cc/output/output_surface.cc
@@ -166,10 +166,6 @@ void OutputSurface::Reshape(const gfx::Size& size, float scale_factor) {
     software_device_->Resize(size, scale_factor);
 }
 
-gfx::Size OutputSurface::SurfaceSize() const {
-  return surface_size_;
-}
-
 void OutputSurface::BindFramebuffer() {
   DCHECK(context_provider_.get());
   context_provider_->ContextGL()->BindFramebuffer(GL_FRAMEBUFFER, 0);
@@ -201,6 +197,10 @@ OverlayCandidateValidator* OutputSurface::GetOverlayCandidateValidator() const {
   return nullptr;
 }
 
+unsigned OutputSurface::GetOverlayTextureId() const {
+  return 0;
+}
+
 void OutputSurface::SetWorkerContextShouldAggressivelyFreeResources(
     bool aggressively_free_resources) {
   TRACE_EVENT1("cc",