Support user-configurable function to create IDWriteFactory

src/utils/win/SkDWrite.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 "SkDWrite.h"
 #include "SkHRESULT.h"
 #include "SkOnce.h"
 #include "SkString.h"
 
 #include <dwrite.h>
 
 static IDWriteFactory* gDWriteFactory = NULL;
+static void (*gDWriteFactoryProc)(IDWriteFactory**) = NULL;
+
+void SkSetDirectWriteFactoryProc(void (*proc)(IDWriteFactory**)) {
+    gDWriteFactoryProc = proc;
+}
 
 static void create_dwrite_factory(IDWriteFactory** factory) {
+    if (gDWriteFactoryProc) {
+        gDWriteFactoryProc(factory);
+        return;
+    }
+
     typedef decltype(DWriteCreateFactory)* DWriteCreateFactoryProc;
     DWriteCreateFactoryProc dWriteCreateFactoryProc = reinterpret_cast<DWriteCreateFactoryProc>(
         GetProcAddress(LoadLibraryW(L"dwrite.dll"), "DWriteCreateFactory"));
 
     if (!dWriteCreateFactoryProc) {
         HRESULT hr = HRESULT_FROM_WIN32(GetLastError());
         if (!IS_ERROR(hr)) {
             hr = ERROR_PROC_NOT_FOUND;
         }
         HRVM(hr, "Could not get DWriteCreateFactory proc.");
@@ skipping 91 matching lines @@
     );
     if (!*proc) {
         HRESULT hr = HRESULT_FROM_WIN32(GetLastError());
         if (!IS_ERROR(hr)) {
             hr = ERROR_PROC_NOT_FOUND;
         }
         return hr;
     }
     return S_OK;
 }