Remove Uint8ClampedArray use from ImageBuffer.h ImageDataBuffer

Source/platform/graphics/ImageBuffer.h

 /*
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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.
@@ skipping 25 matching lines @@
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/GraphicsTypes3D.h"
 #include "platform/graphics/ImageBufferSurface.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 #include "platform/transforms/AffineTransform.h"
 #include "third_party/skia/include/core/SkPaint.h"
 #include "wtf/Forward.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
-#include "wtf/Uint8ClampedArray.h"
 
 namespace WTF {
 
 class ArrayBufferContents;
 
 } // namespace WTF
 
 namespace blink {
 
 class DrawingBuffer;
@@ skipping 97 matching lines @@
     friend class CrossfadeGeneratedImage;
     friend class GradientGeneratedImage;
     friend class SkiaImageFilterBuilder;
 
     OwnPtr<ImageBufferSurface> m_surface;
     OwnPtr<GraphicsContext> m_context;
     ImageBufferClient* m_client;
     OwnPtr<DisplayItemList> m_displayItemList;
 };
 
-struct ImageDataBuffer {
-    ImageDataBuffer(const IntSize& size, PassRefPtr<Uint8ClampedArray> data) : m_size(size), m_data(data) { }
-    IntSize size() const { return m_size; }
-    unsigned char* data() const { return m_data->data(); }
-
-    IntSize m_size;
-    RefPtr<Uint8ClampedArray> m_data;
+struct ImageDataBuffer : public IntSize {

[Yuki, 2015/01/07 13:00:57]

ImageDataBuffer is not a size.  So we shouldn't inherit from IntSize.  Public
inheritance should be used only for is-a relationship, and never for has-a
relationship.

We don't want an ImageDataBuffer to be implicitly casted to IntSize.

[Yuki, 2015/01/07 14:42:06]

It's simply because an image is not a size.  An image has a size (width and
height), image data, etc.  Like a house is not a door, but a house has doors and
windows.

For example,

    class Window {
        Window(String windowTitle, Size windowSize);
    };

    String title = "...";
    Image backgroundImage = ...;
    Window window = new Window(title, backgroundImage);

We'd like a compile error on the last line, because Window's ctor requires a
title and a window size, but we're passing a background image which we'd like to
show in the window.

If we'd like to create a window with the size of the image, then we should
explicitly write:

    Window window = new Window(title, backgroundImage.size());

Then, it's clearer for both of compilers and developers.

[Yuki, 2015/01/08 04:32:38]

If ImageDataBuffer inherits from IntSize, ImageDataBufer can be implicitly
converted to IntSize, and it would cause bugs which are hard to realize.

This is as if we had
    class IntSize {
        IntSize(ImageDataBuffer);  // no "explicit" keyword
    }

This is dangerous, and it's possible to introduce severe bugs.  What I'm afraid
most is that this sort of bugs are hard to find out once it's introduced.

I don't know what consistency you're caring (SkBitmap does not inherit from
SkSize), but I think it's less important.  I don't have no choice on this point.
 This is a famous problem in OOD.

I agree with almost all of your points except for this point.  I'll send a
l-g-t-m once this gets fixed.

+    ImageDataBuffer(const IntSize& size, unsigned char* data) : IntSize(size), m_data(data) { }
+    unsigned char* pixels() const { return m_data; }
+    unsigned char* m_data;
 };
 
 String PLATFORM_EXPORT ImageDataToDataURL(const ImageDataBuffer&, const String& mimeType, const double* quality);
 
 } // namespace blink
 
 #endif // ImageBuffer_h