Use surface copy requests for layout tests.

content/renderer/gpu/render_widget_compositor_delegate.h

Index: content/renderer/gpu/render_widget_compositor_delegate.h
diff --git a/content/renderer/gpu/render_widget_compositor_delegate.h b/content/renderer/gpu/render_widget_compositor_delegate.h
index e31e19e26b56ce8e3178ebd40750049d902e5e58..4ba6fd4811ce73fd645988fe8e03dafb663156a3 100644
--- a/content/renderer/gpu/render_widget_compositor_delegate.h
+++ b/content/renderer/gpu/render_widget_compositor_delegate.h
@@ -12,7 +12,9 @@ struct WebScreenInfo;
 
 namespace cc {
 class BeginFrameSource;
+class CopyOutputRequest;
 class OutputSurface;
+class SwapPromise;
 }
 
 namespace content {
@@ -83,6 +85,11 @@ class CONTENT_EXPORT RenderWidgetCompositorDelegate {
   // perform actual painting work.
   virtual void WillBeginCompositorFrame() = 0;
 
+  // For use in layout test mode only, attempts to copy the full content of the
+  // compositor.
+  virtual std::unique_ptr<cc::SwapPromise> RequestCopyOfOutputForLayoutTest(
+      std::unique_ptr<cc::CopyOutputRequest> request) = 0;
+
  protected:
   virtual ~RenderWidgetCompositorDelegate() {}
 };