Allow custom font collection for DirectWrite font manager.

src/ports/SkFontMgr_win_dw.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTypes.h"
 #if defined(SK_BUILD_FOR_WIN32)
 
@@ skipping 1049 matching lines @@
     SkTScopedComPtr<IDWriteFontFace> fontFace;
     HRNM(font->CreateFontFace(&fontFace), "Could not create font face.");
 
     return fFontMgr->createTypefaceFromDWriteFont(fontFace.get(), font.get(),
                                                   fFontFamily.get());
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 #include "SkTypeface_win.h"
 
-SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory) {
+SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
+                                            IDWriteFontCollection* collection) {
     if (nullptr == factory) {
         factory = sk_get_dwrite_factory();
         if (nullptr == factory) {
             return nullptr;
         }
     }
 
-    SkTScopedComPtr<IDWriteFontCollection> sysFontCollection;
-    HRNM(factory->GetSystemFontCollection(&sysFontCollection, FALSE),
-         "Could not get system font collection.");
+    SkTScopedComPtr<IDWriteFontCollection> systemFontCollection;
+    if (nullptr == collection) {
+        HRNM(factory->GetSystemFontCollection(&systemFontCollection, FALSE),
+             "Could not get system font collection.");
+        collection = systemFontCollection.get();
+    }
 
     WCHAR localeNameStorage[LOCALE_NAME_MAX_LENGTH];
     WCHAR* localeName = nullptr;
     int localeNameLen = 0;
 
     // Dynamically load GetUserDefaultLocaleName function, as it is not available on XP.
     SkGetUserDefaultLocaleNameProc getUserDefaultLocaleNameProc = nullptr;
     HRESULT hr = SkGetGetUserDefaultLocaleNameProc(&getUserDefaultLocaleNameProc);
     if (nullptr == getUserDefaultLocaleNameProc) {
         SK_TRACEHR(hr, "Could not get GetUserDefaultLocaleName.");
     } else {
         localeNameLen = getUserDefaultLocaleNameProc(localeNameStorage, LOCALE_NAME_MAX_LENGTH);
         if (localeNameLen) {
             localeName = localeNameStorage;
         };
     }
 
-    return new SkFontMgr_DirectWrite(factory, sysFontCollection.get(), localeName, localeNameLen);
+    return new SkFontMgr_DirectWrite(factory, collection, localeName, localeNameLen);
 }
 
 #include "SkFontMgr_indirect.h"
 SK_API SkFontMgr* SkFontMgr_New_DirectWriteRenderer(SkRemotableFontMgr* proxy) {
     SkAutoTUnref<SkFontMgr> impl(SkFontMgr_New_DirectWrite());
     if (impl.get() == nullptr) {
         return nullptr;
     }
     return new SkFontMgr_Indirect(impl.get(), proxy);
 }
 #endif//defined(SK_BUILD_FOR_WIN32)