Implement PaintRenderingContext2D off BaseRenderingContext2D

third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PaintRenderingContext2D_h
+#define PaintRenderingContext2D_h
+
+#include "bindings/core/v8/ScriptWrappable.h"
+#include "modules/ModulesExport.h"
+#include "modules/canvas2d/BaseRenderingContext2D.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+
+namespace blink {
+
+class CanvasImageSource;
+class Color;
+class ImageBuffer;
+
+class MODULES_EXPORT PaintRenderingContext2D : public BaseRenderingContext2D, public NoBaseWillBeGarbageCollectedFinalized<PaintRenderingContext2D>, public ScriptWrappable {
+    DEFINE_WRAPPERTYPEINFO();
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(PaintRenderingContext2D);
+    WTF_MAKE_NONCOPYABLE(PaintRenderingContext2D);
+    USING_FAST_MALLOC_WILL_BE_REMOVED(PaintRenderingContext2D);
+public:
+    PassOwnPtrWillBeRawPtr<PaintRenderingContext2D> create(PassOwnPtr<ImageBuffer> imageBuffer)
+    {
+        return adoptPtrWillBeNoop(new PaintRenderingContext2D(imageBuffer));
+    }
+
+    // BaseRenderingContext2D
+
+    // PaintRenderingContext2D doesn't have any pixel readback so the origin
+    // is always clean, and unable to taint it.
+    bool originClean() const final { return true; }

[Justin Novosad, 2016/03/17 18:46:10]

could put ASSERT_NOT_REACHED() here and in wouldTaintOrigin, to certify that the
flags is never queried, which proves that it doe not need to be tracked.

[ikilpatrick, 2016/03/17 19:15:41]

It's actually used a bunch of times inside of BaseRenderingContext2D

wouldTaintOrigin() is used for createPattern - 
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

originClean() is used in most of the draw methods -
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

Added setOriginTainted ASSERT_NOT_REACHED I think makes sense?

+    void setOriginTainted() final { }
+    bool wouldTaintOrigin(CanvasImageSource*) final { return false; }
+
+    int width() const final;
+    int height() const final;
+
+    bool hasImageBuffer() const final { return m_imageBuffer; }
+    ImageBuffer* imageBuffer() const final { return m_imageBuffer.get(); }
+
+    bool parseColorOrCurrentColor(Color&, const String& colorString) const final;
+
+    SkCanvas* drawingCanvas() const final;
+    SkCanvas* existingDrawingCanvas() const final;
+    void disableDeferral(DisableDeferralReason) final { }
+
+    AffineTransform baseTransform() const final;
+
+    void didDraw(const SkIRect& dirtyRect) final;
+
+    // TODO(ikilpatrick): We'll need to either only accept resolved filters
+    // from a typed-om <filter> object, or use the appropriate style resolution
+    // host to determine 'em' units etc in filters. At the moment just pretend

[Justin Novosad, 2016/03/17 18:46:10]

You could just specify built-in defaults

[ikilpatrick, 2016/03/17 19:15:42]

Sorry, I fall off quickly when it comes to filters, what would the defaults be?

+    // that we don't have a filter set.
+    bool stateHasFilter() final { return false; }
+    SkImageFilter* stateGetFilter() final { return nullptr; }
+
+    void validateStateStack() final;
+
+    bool hasAlpha() const final { return true; }
+
+    // PaintRenderingContext2D cannot lose it's context.
+    bool isContextLost() const final { return false; }
+
+private:
+    explicit PaintRenderingContext2D(PassOwnPtr<ImageBuffer>);
+
+    OwnPtr<ImageBuffer> m_imageBuffer;
+};
+
+} // namespace blink
+
+#endif // PaintRenderingContext2D_h