Add canvas blending modes under a runtime flag

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

Index: Source/core/platform/graphics/skia/ImageSkia.cpp
diff --git a/Source/core/platform/graphics/skia/ImageSkia.cpp b/Source/core/platform/graphics/skia/ImageSkia.cpp
index 92a0fb7f5cd11d1ebd3ef1a20894951f37b88ee5..88b804ba427871ecfe68db0fe0a5894bf28ca472 100644
--- a/Source/core/platform/graphics/skia/ImageSkia.cpp
+++ b/Source/core/platform/graphics/skia/ImageSkia.cpp
@@ -609,7 +609,7 @@ void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dstRect, const Fl
     draw(ctxt, dstRect, srcRect, colorSpace, compositeOp, blendMode, DoNotRespectImageOrientation);
 }
 
-void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dstRect, const FloatRect& srcRect, ColorSpace colorSpace, CompositeOperator compositeOp, BlendMode, RespectImageOrientationEnum shouldRespectImageOrientation)
+void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dstRect, const FloatRect& srcRect, ColorSpace colorSpace, CompositeOperator compositeOp, BlendMode blendMode, RespectImageOrientationEnum shouldRespectImageOrientation)
 {
     // Spin the animation to the correct frame before we try to draw it, so we
     // don't draw an old frame and then immediately need to draw a newer one,
@@ -648,7 +648,7 @@ void BitmapImage::draw(GraphicsContext* ctxt, const FloatRect& dstRect, const Fl
         }
     }
 
-    paintSkBitmap(ctxt, *bm, normSrcRect, normDstRect, WebCoreCompositeToSkiaComposite(compositeOp));
+    paintSkBitmap(ctxt, *bm, normSrcRect, normDstRect, WebCoreCompositeToSkiaComposite(compositeOp, blendMode));
 
     if (ImageObserver* observer = imageObserver())
         observer->didDraw(this);