Fix subpixel font scaling for DirectWrite

Source/platform/fonts/win/FontCacheSkiaWin.cpp

 /*
  * Copyright (C) 2006, 2007 Apple Computer, Inc.
  * Copyright (c) 2006, 2007, 2008, 2009, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 43 matching lines @@
     s_sideloadedFonts->set(name.c_str(), typeface);
 }
 
 FontCache::FontCache()
     : m_purgePreventCount(0)
 {
     SkFontMgr* fontManager;
 
     if (s_useDirectWrite) {
         fontManager = SkFontMgr_New_DirectWrite(s_directWriteFactory);
+        s_useSubpixelPositioning = RuntimeEnabledFeatures::subpixelFontScalingEnabled();
     } else {
         fontManager = SkFontMgr_New_GDI();
         // Subpixel text positioning is not supported by the GDI backend.
         s_useSubpixelPositioning = false;
     }
 
     ASSERT(fontManager);
     m_fontManager = adoptPtr(fontManager);
 }
 
@@ skipping 202 matching lines @@
         result->setMinSizeForAntiAlias(
             minSizeForAntiAlias(fontDescription.script()));
         if (fontRequiresFullHinting(family))
             result->setHinting(SkPaint::kFull_Hinting);
     }
 
     return result;
 }
 
 }