Make DisplayItemClient an interface

third_party/WebKit/Source/core/svg/graphics/SVGImage.h

 /*
  * Copyright (C) 2006 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 24 matching lines @@
 
 namespace blink {
 
 class Document;
 class FrameView;
 class Page;
 class LayoutBox;
 class SVGImageChromeClient;
 class SVGImageForContainer;
 
-class SVGImage final : public Image {
+class SVGImage final : public Image, public DisplayItemClient {

[pdr., 2015/12/05 21:39:19]

This could be problematic because a single SVGImage can be shared by multiple
documents since it lives in the memorycache. For example, if two tabs both
reference happy.svg, and the two tabs happen to be in the same process, they
will share one SVGImage instance.

It looks like SVGImage is only a superclass of DisplayItemClient for two
SkPictureBuilder calls. Can we switch those to use a null DisplayItemClient* so
SVGImage doesn't need to be a DisplayItemClient?

[Xianzhu, 2015/12/07 17:14:00]

If you meant the problem that the invalidation bits would be modified by
different PaintControllers, I think it can be avoided by adding a
CacheableDisplayItemClient type which contains methods for accessing
invalidation bits, while SVGImage can be still a normal non-cacheable
DisplayItemClient.     
I don't quite understand the use cases you mentioned. Can you provide links to
the code?

The current patch requires non-null DisplayItemClients. Null DisplayItemClient
seems to increase complexity and eliminate the ability to track display item
sources for debugging.

 public:
     static PassRefPtr<SVGImage> create(ImageObserver* observer)
     {
         return adoptRef(new SVGImage(observer));
     }
 
     static bool isInSVGImage(const Node*);
 
     LayoutBox* embeddedContentBox() const;
 
@@ skipping 14 matching lines @@
     PassRefPtr<SkImage> imageForCurrentFrame() override;
 
     // Returns the SVG image document's frame.
     FrameView* frameView() const;
 
     // Does the SVG image/document contain any animations?
     bool hasAnimations() const;
 
     void updateUseCounters(Document&) const;
 
-    DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
-    String debugName() const { return "SVGImage"; }
+    String debugName() const final { return "SVGImage"; }
 
 private:
     friend class AXLayoutObject;
     friend class SVGImageChromeClient;
     friend class SVGImageForContainer;
 
     ~SVGImage() override;
 
     String filenameExtension() const override;
 
@@ skipping 42 matching lines @@
         m_image->setImageObserver(m_observer);
     }
 private:
     Image* m_image;
     ImageObserver* m_observer;
 };
 
 }
 
 #endif // SVGImage_h