Implement the logic to kick off image decoding jobs for TileManager

cc/picture.h

Index: cc/picture.h
diff --git a/cc/picture.h b/cc/picture.h
index b555eb048fa5914d5de08c512783aade42cac086..385ee772dbabd6b048e0de0d9ac61d5a1240eb3c 100644
--- a/cc/picture.h
+++ b/cc/picture.h
@@ -5,11 +5,14 @@
 #ifndef CC_PICTURE_H_
 #define CC_PICTURE_H_
 
+#include <vector>
+
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "cc/cc_export.h"
 #include "skia/ext/refptr.h"
 #include "third_party/skia/include/core/SkPicture.h"
+#include "third_party/skia/include/core/SkPixelRef.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
@@ -39,6 +42,8 @@ public:
   // Assumes contentsScale have already been applied.
   void Raster(SkCanvas* canvas);
 
+  std::vector<SkPixelRef*> GatherPixelRefs(const gfx::Rect& rect);
+
 private:
   Picture(gfx::Rect layer_rect);
   // This constructor assumes SkPicture is already ref'd and transfers