Add canvas blending modes under a runtime flag

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

Index: Source/core/platform/graphics/skia/ImageBufferSkia.cpp
diff --git a/Source/core/platform/graphics/skia/ImageBufferSkia.cpp b/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
index f73e044a5ad4ea34027b051b16e2a689f278bd9a..bfd6cd337e087da213479fd17be14c8bd5e9e767 100644
--- a/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
+++ b/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
@@ -258,11 +258,11 @@ static bool drawNeedsCopy(GraphicsContext* src, GraphicsContext* dst)
 }
 
 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_context->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);
 }
 
 void ImageBuffer::drawPattern(GraphicsContext* context, const FloatRect& srcRect, const AffineTransform& patternTransform,