Draw thin slices of an image w/ anti-aliasing for 2D <canvas>

Source/platform/graphics/GraphicsContext.h

Index: Source/platform/graphics/GraphicsContext.h
diff --git a/Source/platform/graphics/GraphicsContext.h b/Source/platform/graphics/GraphicsContext.h
index add6d3c26e59a1e6324dce9fc15eb4094038e3fd..d33c2319fbe0e0d783236d33c89c1787c8c47ec2 100644
--- a/Source/platform/graphics/GraphicsContext.h
+++ b/Source/platform/graphics/GraphicsContext.h
@@ -136,6 +136,11 @@ public:
     void setShouldAntialias(bool antialias) { mutableState()->setShouldAntialias(antialias); }
     bool shouldAntialias() const { return immutableState()->shouldAntialias(); }
 
+    // Disable the optimization that disables anti-aliasing for

[Justin Novosad, 2014/04/01 17:02:01]

Double negation: Disabling the disabling is more confusing than necessary.
Also, there should be some warning that determining whether an image is hairline
is only reliable when the device pixel scale is fixed (e.g. when drawing to an
ImageBuffer).  Therefore, this option should not be used on GraphicsContexts
that are backed by a recording canvas.  You could even add a safety check:
ASSERT(!isRecording());

[fs, 2014/04/02 08:31:37]

Made this read more like the name of the method.
Added a "Note" and the ASSERT.

+    // scale/multiple-of-90-degrees rotation for thin ("hairline") images.
+    void disableAntialiasingOptimizationForHairlineImages() { m_antialiasHairlineImages = true; }
+    bool shouldAntialiasHairlineImages() const { return m_antialiasHairlineImages; }
+
     void setShouldClampToSourceRect(bool clampToSourceRect) { mutableState()->setShouldClampToSourceRect(clampToSourceRect); }
     bool shouldClampToSourceRect() const { return immutableState()->shouldClampToSourceRect(); }
 
@@ -504,6 +509,7 @@ private:
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
+    bool m_antialiasHairlineImages : 1;
 };
 
 } // namespace WebCore