Support user-configurable function to create IDWriteFactory

include/ports/SkTypeface_win.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTypeface_win_DEFINED
 #define SkTypeface_win_DEFINED
 
@@ skipping 15 matching lines @@
 SK_API void SkLOGFONTFromTypeface(const SkTypeface* typeface, LOGFONT* lf);
 
 /**
   *  Set an optional callback to ensure that the data behind a LOGFONT is loaded.
   *  This will get called if Skia tries to access the data but hits a failure.
   *  Normally this is null, and is only required if the font data needs to be
   *  remotely (re)loaded.
   */
 SK_API void SkTypeface_SetEnsureLOGFONTAccessibleProc(void (*)(const LOGFONT&));
 
+/**
+ * Set an optional callback to allow the user to create the IDWriteFactory.
+ */
+struct IDWriteFactory;
+SK_API void SkSetDirectWriteFactoryProc(void (*)(IDWriteFactory**));
+
 // Experimental!
 //
 class SkFontMgr;
 class SkRemotableFontMgr;
 
 SK_API SkFontMgr* SkFontMgr_New_GDI();
 SK_API SkFontMgr* SkFontMgr_New_DirectWrite();
 
 /**
  *  Creates an SkFontMgr which renders using DirectWrite and obtains its data
  *  from the SkRemotableFontMgr.
  *
  *  If DirectWrite could not be initialized, will return NULL.
  */
 SK_API SkFontMgr* SkFontMgr_New_DirectWriteRenderer(SkRemotableFontMgr*);
 
 /**
  *  Creates an SkRemotableFontMgr backed by DirectWrite using the default
  *  system font collection in the current locale.
  *
  *  If DirectWrite could not be initialized, will return NULL.
  */
 SK_API SkRemotableFontMgr* SkRemotableFontMgr_New_DirectWrite();
 
 #endif