Revert "Change call-sites now that SkCanvas is not ref-counted"

cc/playback/discardable_image_map.h

Index: cc/playback/discardable_image_map.h
diff --git a/cc/playback/discardable_image_map.h b/cc/playback/discardable_image_map.h
index c773a7237057e7cb9c886a81f039e290c6088248..f2e91aedc2f128d8b3fafcd212acde4eb5cda9ab 100644
--- a/cc/playback/discardable_image_map.h
+++ b/cc/playback/discardable_image_map.h
@@ -41,7 +41,7 @@ class CC_EXPORT DiscardableImageMap {
 
    private:
     DiscardableImageMap* image_map_;
-    std::unique_ptr<SkCanvas> metadata_canvas_;
+    sk_sp<SkCanvas> metadata_canvas_;
   };
 
   DiscardableImageMap();
@@ -57,7 +57,7 @@ class CC_EXPORT DiscardableImageMap {
   friend class ScopedMetadataGenerator;
   friend class DiscardableImageMapTest;
 
-  std::unique_ptr<SkCanvas> BeginGeneratingMetadata(const gfx::Size& bounds);
+  sk_sp<SkCanvas> BeginGeneratingMetadata(const gfx::Size& bounds);
   void EndGeneratingMetadata();
 
   std::vector<std::pair<DrawImage, gfx::Rect>> all_images_;