Add option to specify font fallback when creating the skia font manager

include/ports/SkTypeface_win.h

Index: include/ports/SkTypeface_win.h
diff --git a/include/ports/SkTypeface_win.h b/include/ports/SkTypeface_win.h
index da728ca3c0cfc635a4f79cd209ed13e2ae26115a..e18ed93341e0d3a90f6857e5bb74433733301600 100644
--- a/include/ports/SkTypeface_win.h
+++ b/include/ports/SkTypeface_win.h
@@ -41,10 +41,14 @@ class SkFontMgr;
 class SkRemotableFontMgr;
 struct IDWriteFactory;
 struct IDWriteFontCollection;
+struct IDWriteFontFallback;
 
 SK_API SkFontMgr* SkFontMgr_New_GDI();
 SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory = NULL,
                                             IDWriteFontCollection* collection = NULL);
+SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
+                                            IDWriteFontCollection* collection,
+                                            IDWriteFontFallback* fallback);
 
 /**
  *  Creates an SkFontMgr which renders using DirectWrite and obtains its data