cc: Update discardable image metadata generation to get PaintImages.

cc/paint/paint_op_buffer.h

Index: cc/paint/paint_op_buffer.h
diff --git a/cc/paint/paint_op_buffer.h b/cc/paint/paint_op_buffer.h
index 714f4ef0f2fd656af7d35aad3d50df82fd10483f..c045a0e86234f6123e55a684157eddb33038e046 100644
--- a/cc/paint/paint_op_buffer.h
+++ b/cc/paint/paint_op_buffer.h
@@ -9,6 +9,7 @@
 
 #include "base/logging.h"
 #include "base/memory/aligned_memory.h"
+#include "cc/paint/discardable_image_map.h"
 #include "cc/paint/paint_canvas.h"
 #include "cc/paint/paint_export.h"
 #include "cc/paint/paint_flags.h"
@@ -20,7 +21,7 @@
 // See: third_party/skia/src/core/SkLiteDL.h.
 
 namespace cc {
-
+class DiscardableImageStore;
 class DisplayItemList;
 
 class CC_PAINT_EXPORT ThreadsafeMatrix : public SkMatrix {
@@ -576,6 +577,7 @@ class CC_PAINT_EXPORT PaintOpBuffer : public SkRefCnt {
   }
   int numSlowPaths() const { return num_slow_paths_; }
   bool HasDiscardableImages() const { return has_discardable_images_; }
+  void GatherDiscardableImages(DiscardableImageStore* image_store) const;
 
   // Resize the PaintOpBuffer to exactly fit the current amount of used space.
   void ShrinkToFit();