cc: Only add surface ID to embedded_surfaces if fallback does not match

cc/layers/surface_layer_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/surface_layer_impl.h"
 
 #include <stdint.h>
 
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/debug/debug_colors.h"
@@ skipping 47 matching lines @@
   LayerImpl::PushPropertiesTo(layer);
   SurfaceLayerImpl* layer_impl = static_cast<SurfaceLayerImpl*>(layer);
   layer_impl->SetPrimarySurfaceInfo(primary_surface_info_);
   layer_impl->SetFallbackSurfaceInfo(fallback_surface_info_);
   layer_impl->SetStretchContentToFillBounds(stretch_content_to_fill_bounds_);
 }
 
 void SurfaceLayerImpl::AppendQuads(RenderPass* render_pass,
                                    AppendQuadsData* append_quads_data) {
   AppendRainbowDebugBorder(render_pass);
+  bool needs_synchronization =

[danakj, 2017/05/04 19:14:08]

nit: needs_fallback?

[Fady Samuel, 2017/05/04 20:03:48]

Done.

+      fallback_surface_info_.id() != primary_surface_info_.id();
   auto* primary = CreateSurfaceDrawQuad(
       render_pass, SurfaceDrawQuadType::PRIMARY, primary_surface_info_,
-      &append_quads_data->embedded_surfaces);
+      needs_synchronization ? &append_quads_data->embedded_surfaces : nullptr);

[danakj, 2017/05/04 19:14:08]

The side effects here are very unclear, with the relationship that this is
preventing embedded surfaces from adding the the surface id. Proposal: Remove
the |embedded_surfaces| from CreateSurfaceDrawQuad, and do the push_back here
directly instead.

[Fady Samuel, 2017/05/04 20:03:48]

Done.

   // Emitting a fallback SurfaceDrawQuad is unnecessary if the primary and
   // fallback surface Ids match.
-  if (primary && fallback_surface_info_.id() != primary_surface_info_.id()) {
+  if (primary && needs_synchronization) {
     primary->fallback_quad = CreateSurfaceDrawQuad(
         render_pass, SurfaceDrawQuadType::FALLBACK, fallback_surface_info_,
         nullptr /* embedded_surfaces */);
   }
 }
 
 SurfaceDrawQuad* SurfaceLayerImpl::CreateSurfaceDrawQuad(
     RenderPass* render_pass,
     SurfaceDrawQuadType surface_draw_quad_type,
     const SurfaceInfo& surface_info,
@@ skipping 142 matching lines @@
   dict->SetString("surface_id", primary_surface_info_.id().ToString());
   dict->SetString("fallback_surface_id",
                   fallback_surface_info_.id().ToString());
 }
 
 const char* SurfaceLayerImpl::LayerTypeAsString() const {
   return "cc::SurfaceLayerImpl";
 }
 
 }  // namespace cc