cc: Async readback.

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index 84119649773f43d3e1decfa18041c772ad49e81e..a35d7a5df308255829ab2c3a62c1c5346756f618 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "cc/animation/layer_animation_controller.h"
@@ -76,6 +77,18 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
   const LayerList& children() const { return children_; }
   Layer* child_at(size_t index) { return children_[index].get(); }
 
+  typedef base::Callback<void(scoped_ptr<SkBitmap>)>
+      RequestCopyAsBitmapCallback;
+
+  // This requests the layer and its subtree be rendered into an SkBitmap and
+  // call the given callback when the SkBitmap has been produced. If the copy
+  // is unable to be produced (the layer is destroyed first), then the callback
+  // is called with a NULL bitmap.
+  void RequestCopyAsBitmap(RequestCopyAsBitmapCallback callback);
+  bool HasRequestCopyCallback() const {
+    return !request_copy_callbacks_.empty();
+  }
+
   void SetAnchorPoint(gfx::PointF anchor_point);
   gfx::PointF anchor_point() const { return anchor_point_; }
 
@@ -480,6 +493,8 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
 
   gfx::Transform impl_transform_;
 
+  std::vector<RequestCopyAsBitmapCallback> request_copy_callbacks_;
+
   WebKit::WebLayerScrollClient* layer_scroll_client_;
 
   DrawProperties<Layer, RenderSurface> draw_properties_;