Allow WebExternalTextureLayers to receive a bitmap along with a mailbox

cc/output/software_renderer.cc

 // Copyright 2012 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/output/software_renderer.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/compositor_frame_ack.h"
@@ skipping 60 matching lines @@
         resource_provider_->best_texture_format();
   }
   capabilities_.using_set_visibility = true;
   // The updater can access bitmaps while the SoftwareRenderer is using them.
   capabilities_.allow_partial_texture_updates = true;
   capabilities_.using_partial_swap = true;
 
   capabilities_.using_map_image =
       Settings().use_map_image &&
       output_surface->capabilities().deferred_gl_initialization;
+  capabilities_.using_shared_memory_resources = true;
 }
 
 SoftwareRenderer::~SoftwareRenderer() {}
 
 const RendererCapabilities& SoftwareRenderer::Capabilities() const {
   return capabilities_;
 }
 
 void SoftwareRenderer::BeginDrawingFrame(DrawingFrame* frame) {
   TRACE_EVENT0("cc", "SoftwareRenderer::BeginDrawingFrame");
@@ skipping 399 matching lines @@
   visible_ = visible;
 }
 
 void SoftwareRenderer::SetDiscardBackBufferWhenNotVisible(bool discard) {
   // TODO(piman, skaslev): Can we release the backbuffer? We don't currently
   // receive memory policy yet anyway.
   NOTIMPLEMENTED();
 }
 
 }  // namespace cc