Add canvas blending modes under a runtime flag

Source/WebCore/platform/graphics/skia/ImageBufferSkia.cpp

Index: Source/WebCore/platform/graphics/skia/ImageBufferSkia.cpp
===================================================================
--- Source/WebCore/platform/graphics/skia/ImageBufferSkia.cpp	(revision 147814)
+++ Source/WebCore/platform/graphics/skia/ImageBufferSkia.cpp	(working copy)
@@ -267,11 +267,11 @@
 }
 
 void ImageBuffer::draw(GraphicsContext* context, ColorSpace styleColorSpace, const FloatRect& destRect, const FloatRect& srcRect,
-    CompositeOperator op, BlendMode, bool useLowQualityScale)
+    CompositeOperator op, BlendMode blendMode, bool useLowQualityScale)
 {
     const SkBitmap& bitmap = *m_data.m_platformContext.bitmap();
     RefPtr<Image> image = BitmapImage::create(NativeImageSkia::create(drawNeedsCopy(m_context.get(), context) ? deepSkBitmapCopy(bitmap) : bitmap));
-    context->drawImage(image.get(), styleColorSpace, destRect, srcRect, op, DoNotRespectImageOrientation, useLowQualityScale);
+    context->drawImage(image.get(), styleColorSpace, destRect, srcRect, op, blendMode, DoNotRespectImageOrientation, useLowQualityScale);

[Stephen Chennney, 2013/04/08 16:07:02]

Does this change make some version of drawImage no-longer-used? If so, the
no-longer-used version should be removed.

[rosca, 2013/04/08 19:53:25]

I removed one of the GraphicsContext::drawImage methods.

 }
 
 void ImageBuffer::drawPattern(GraphicsContext* context, const FloatRect& srcRect, const AffineTransform& patternTransform,