cc: Update discardable image metadata generation to get PaintImages.

cc/paint/discardable_image_map.h

Index: cc/paint/discardable_image_map.h
diff --git a/cc/paint/discardable_image_map.h b/cc/paint/discardable_image_map.h
index 5a84fb8391cb14155e5a5c170fc5a9fae1cb984c..881698fdac797f4b7f36ae3153f66697ac7170d5 100644
--- a/cc/paint/discardable_image_map.h
+++ b/cc/paint/discardable_image_map.h
@@ -13,15 +13,15 @@
 #include "cc/paint/draw_image.h"
 #include "cc/paint/image_id.h"
 #include "cc/paint/paint_export.h"
+#include "cc/paint/paint_flags.h"
+#include "cc/paint/paint_image.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace cc {
-
-// Helper function to apply the matrix to the rect and return the result.
-SkRect MapRect(const SkMatrix& matrix, const SkRect& src);
+class DiscardableImageStore;
 
 // This class is used for generating discardable images data (see DrawImage
 // for the type of data it stores). It allows the client to query a particular
@@ -34,11 +34,11 @@ class CC_PAINT_EXPORT DiscardableImageMap {
                             const gfx::Size& bounds);
     ~ScopedMetadataGenerator();
 
-    SkCanvas* canvas() { return metadata_canvas_.get(); }
+    DiscardableImageStore* image_store() { return image_store_.get(); }
 
    private:
     DiscardableImageMap* image_map_;
-    std::unique_ptr<SkCanvas> metadata_canvas_;
+    std::unique_ptr<DiscardableImageStore> image_store_;
   };
 
   DiscardableImageMap();
@@ -55,7 +55,8 @@ class CC_PAINT_EXPORT DiscardableImageMap {
   friend class ScopedMetadataGenerator;
   friend class DiscardableImageMapTest;
 
-  std::unique_ptr<SkCanvas> BeginGeneratingMetadata(const gfx::Size& bounds);
+  std::unique_ptr<DiscardableImageStore> BeginGeneratingMetadata(
+      const gfx::Size& bounds);
   void EndGeneratingMetadata();
 
   std::vector<std::pair<DrawImage, gfx::Rect>> all_images_;