Add ability to pass through IDWriteFactory so sandbox can control how it's constructed

Source/web/win/WebFontRendering.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 "public/web/win/WebFontRendering.h"
 
 #include "platform/fonts/FontCache.h"
 
 namespace blink {
 
 // static
 void WebFontRendering::setUseDirectWrite(bool useDirectWrite)
 {
     WebCore::FontCache::setUseDirectWrite(useDirectWrite);
 }
 
 // static
+void WebFontRendering::setDirectWriteFactory(IDWriteFactory* factory)
+{
+    WebCore::FontCache::setDirectWriteFactory(factory);
+}
+
+// static
 void WebFontRendering::setUseSubpixelPositioning(bool useSubpixelPositioning)
 {
     WebCore::FontCache::setUseSubpixelPositioning(useSubpixelPositioning);
 }
 
 } // namespace blink