Addding support for -webkit-background-blend-mode to blink.

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 88b804ba427871ecfe68db0fe0a5894bf28ca472..c3cd3cc9632490dc72d4722bfb4e0019318462c6 100644
--- a/Source/core/platform/graphics/skia/ImageSkia.cpp
+++ b/Source/core/platform/graphics/skia/ImageSkia.cpp
@@ -456,7 +456,7 @@ void Image::drawPattern(GraphicsContext* context,
                         ColorSpace styleColorSpace,
                         CompositeOperator compositeOp,
                         const FloatRect& destRect,
-                        BlendMode)
+                        BlendMode blendMode)
 {
     TRACE_EVENT0("skia", "Image::drawPattern");
     RefPtr<NativeImageSkia> bitmap = nativeImageForCurrentFrame();
@@ -536,7 +536,8 @@ void Image::drawPattern(GraphicsContext* context,
 
     SkPaint paint;
     paint.setShader(shader)->unref();
-    paint.setXfermodeMode(WebCoreCompositeToSkiaComposite(compositeOp));
+    paint.setXfermodeMode(WebCoreCompositeToSkiaComposite(compositeOp, blendMode));
+
     paint.setFilterBitmap(resampling == RESAMPLE_LINEAR);
 
     context->drawRect(destRect, paint);