Make beginLayer() and CanvasRenderingContext2D use SkXfermode::Mode.

Source/platform/graphics/paint/FilterDisplayItem.cpp

Index: Source/platform/graphics/paint/FilterDisplayItem.cpp
diff --git a/Source/platform/graphics/paint/FilterDisplayItem.cpp b/Source/platform/graphics/paint/FilterDisplayItem.cpp
index bd6aab99ce8ce65077fe18c45ca045337f0d3ab1..9d76a800a83e20dc86f7f2aecbfce43832a0bb1c 100644
--- a/Source/platform/graphics/paint/FilterDisplayItem.cpp
+++ b/Source/platform/graphics/paint/FilterDisplayItem.cpp
@@ -16,7 +16,7 @@ void BeginFilterDisplayItem::replay(GraphicsContext* context)
     FloatRect boundaries = mapImageFilterRect(m_imageFilter.get(), m_bounds);
     context->translate(m_bounds.x().toFloat(), m_bounds.y().toFloat());
     boundaries.move(-m_bounds.x().toFloat(), -m_bounds.y().toFloat());
-    context->beginLayer(1, CompositeSourceOver, &boundaries, ColorFilterNone, m_imageFilter.get());
+    context->beginLayer(1, SkXfermode::kSrcOver_Mode, &boundaries, ColorFilterNone, m_imageFilter.get());
     context->translate(-m_bounds.x().toFloat(), -m_bounds.y().toFloat());
 }