Use surface copy requests for layout tests.

content/renderer/layout_test_dependencies.h

Index: content/renderer/layout_test_dependencies.h
diff --git a/content/renderer/layout_test_dependencies.h b/content/renderer/layout_test_dependencies.h
index 743c61d2c7a43ce198342f5ad6e57d179f3e69a5..4b2691a6cf9bc0fd13164a066d863aae144aef7c 100644
--- a/content/renderer/layout_test_dependencies.h
+++ b/content/renderer/layout_test_dependencies.h
@@ -12,7 +12,9 @@
 
 namespace cc {
 class ContextProvider;
+class CopyOutputRequest;
 class OutputSurface;
+class SwapPromise;
 }
 
 namespace gpu {
@@ -27,10 +29,16 @@ class CompositorDependencies;
 class LayoutTestDependencies {
  public:
   virtual std::unique_ptr<cc::OutputSurface> CreateOutputSurface(
+      int32_t routing_id,
       scoped_refptr<gpu::GpuChannelHost> gpu_channel,
       scoped_refptr<cc::ContextProvider> compositor_context_provider,
       scoped_refptr<cc::ContextProvider> worker_context_provider,
       CompositorDependencies* deps) = 0;
+
+  // Returns a SwapPromise which should be queued for the appropriate frame.

[danakj, 2016/07/22 20:50:26]

appropriate = the next compositor frame?

[jbroman, 2016/07/25 18:50:55]

Technically no (you could hold on to this and wait until the frame you want to
take a screenshot), but in practice yes, so I'll change the comment as you
suggested.

+  virtual std::unique_ptr<cc::SwapPromise> RequestCopyOfOutput(
+      int32_t routing_id,
+      std::unique_ptr<cc::CopyOutputRequest> request) = 0;
 };
 
 }  // namespace content