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

Source/platform/graphics/paint/CompositingDisplayItem.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/graphics/paint/CompositingDisplayItem.h"
 
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
+#include "platform/graphics/skia/SkiaUtils.h"
 #include "public/platform/WebDisplayItemList.h"
 
 namespace blink {
 
 void BeginCompositingDisplayItem::replay(GraphicsContext* context)
 {
     context->setCompositeOperation(m_preCompositeOp, m_preBlendMode);
-    context->beginLayer(m_opacity, m_preCompositeOp);
+    context->beginLayer(m_opacity, WebCoreCompositeToSkiaComposite(m_preCompositeOp, m_preBlendMode));
     context->setCompositeOperation(m_postCompositeOp, WebBlendModeNormal);
 }
 
 void BeginCompositingDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
     // FIXME: Change this to appendCompositingItem.
     list->appendTransparencyItem(m_opacity, m_preBlendMode);
 }
 
 #ifndef NDEBUG
 void BeginCompositingDisplayItem::dumpPropertiesAsDebugString(WTF::StringBuilder& stringBuilder) const
 {
     DisplayItem::dumpPropertiesAsDebugString(stringBuilder);
     stringBuilder.append(WTF::String::format(", preCompositingOp: %d, preBlendMode: %d, opacity: %f, postCompositingOp: %d", m_preCompositeOp, m_preBlendMode, m_opacity, m_postCompositeOp));
 }
 #endif
 
 void EndCompositingDisplayItem::replay(GraphicsContext* context)
 {
     context->endLayer();
 }
 
 void EndCompositingDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
     // FIXME: Change this to appendEndCompositingItem.
     list->appendEndTransparencyItem();
 }
 
 } // namespace blink