cc: Allow output readback/copy requests to specify a sub-rect to copy.

cc/output/copy_output_request.h

Index: cc/output/copy_output_request.h
diff --git a/cc/output/copy_output_request.h b/cc/output/copy_output_request.h
index 54fff1a6d66af3de604f04665be21406bb1fa21d..b7eb0b4ffc5bada59e6eb5f2bf5f6b56c50b7e35 100644
--- a/cc/output/copy_output_request.h
+++ b/cc/output/copy_output_request.h
@@ -8,7 +8,7 @@
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
-#include "ui/gfx/size.h"
+#include "ui/gfx/rect.h"
 
 class SkBitmap;
 
@@ -35,15 +35,29 @@ class CC_EXPORT CopyOutputRequest {
   static scoped_ptr<CopyOutputRequest> CreateRelayRequest(
       const CopyOutputRequest& original_request,
       const CopyOutputRequestCallback& result_callback) {
-    return make_scoped_ptr(new CopyOutputRequest(
-        original_request.force_bitmap_result(), result_callback));
+    scoped_ptr<CopyOutputRequest> relay = CreateRequest(result_callback);
+    relay->force_bitmap_result_ = original_request.force_bitmap_result_;
+    relay->has_area_ = original_request.has_area_;
+    relay->area_ = original_request.area_;
+    return relay.Pass();
   }
 
   ~CopyOutputRequest();
 
   bool IsEmpty() const { return result_callback_.is_null(); }
+
   bool force_bitmap_result() const { return force_bitmap_result_; }
 
+  // By default copy requests copy the entire layer's subtree output. If an
+  // area is given, then the intersection of this rect (in layer space) with
+  // the layer's subtree output will be returned.
+  void set_area(gfx::Rect area) {
+    has_area_ = true;
+    area_ = area;
+  }
+  bool has_area() const { return has_area_; }
+  gfx::Rect area() const { return area_; }
+
   void SendResult(scoped_ptr<CopyOutputResult> result);
   void SendBitmapResult(scoped_ptr<SkBitmap> bitmap);
   void SendTextureResult(gfx::Size size,
@@ -60,6 +74,8 @@ class CC_EXPORT CopyOutputRequest {
                              const CopyOutputRequestCallback& result_callback);
 
   bool force_bitmap_result_;
+  bool has_area_;
+  gfx::Rect area_;
   CopyOutputRequestCallback result_callback_;
 };