Add runtime flag for using DirectWrite on windows

Source/core/platform/graphics/skia/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 14 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/platform/graphics/FontCache.h"
 
+#include "RuntimeEnabledFeatures.h"
 #include "SkFontMgr.h"
 #include "SkTypeface_win.h"
 #include "platform/NotImplemented.h"
 #include "core/platform/graphics/Font.h"
 #include "core/platform/graphics/SimpleFontData.h"
 #include "core/platform/graphics/chromium/FontPlatformDataChromiumWin.h"
 #include "core/platform/graphics/chromium/FontUtilsChromiumWin.h"
 
 namespace WebCore {
 
 FontCache::FontCache()
     : m_purgePreventCount(0)
 {
-    m_fontManager = adoptPtr(SkFontMgr_New_GDI());
+    SkFontMgr* fontManager = 0;
+
+    // Prefer DirectWrite (if runtime feature is enabled) but fallback
+    // to GDI on platforms where DirectWrite is not supported.
+    if (RuntimeEnabledFeatures::directWriteEnabled())
+        fontManager = SkFontMgr_New_DirectWrite();
+    if (!fontManager)
+        fontManager = SkFontMgr_New_GDI();
+
+    m_fontManager = adoptPtr(fontManager);
 }
 
 
 static bool fontContainsCharacter(const FontPlatformData* fontData, const wchar_t* family, UChar32 character)
 {
     SkPaint paint;
     fontData->setupPaint(&paint);
     paint.setTextEncoding(SkPaint::kUTF32_TextEncoding);
 
     uint16_t glyph;
@@ skipping 151 matching lines @@
         name.data(),
         fontDescription.computedSize(),
         fontDescription.weight() >= FontWeightBold && !tf->isBold(),
         fontDescription.italic() && !tf->isItalic(),
         fontDescription.orientation());
     tf->unref();
     return result;
 }
 
 }