cc: Async readback.

cc/quads/render_pass.h

Index: cc/quads/render_pass.h
diff --git a/cc/quads/render_pass.h b/cc/quads/render_pass.h
index bfd0d831a8c5b9bd82053a1a91ca0afa68f5c08b..d70232d179d6c1ad9686f9763cd28ea77fadb570 100644
--- a/cc/quads/render_pass.h
+++ b/cc/quads/render_pass.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/hash_pair.h"
 #include "cc/base/scoped_ptr_hash_map.h"
@@ -97,6 +98,14 @@ class CC_EXPORT RenderPass {
   // complete, since they are occluded.
   bool has_occlusion_from_outside_target_surface;
 
+  // If non-empty, the renderer should produce a copy of the render pass'
+  // contents as a bitmap, and give a copy of the bitmap to each callback in
+  // this list. This property should not be serialized between compositors, as
+  // it only makes sense in the root compositor.
+  typedef base::Callback<void(scoped_ptr<SkBitmap>)> 
+      RequestCopyAsBitmapCallback;
+  std::vector<RequestCopyAsBitmapCallback> copy_callbacks;
+
   QuadList quad_list;
   SharedQuadStateList shared_quad_state_list;