Use ChildThreadImpl::thread_safe_sender in font proxy if available

content/child/dwrite_font_proxy/dwrite_font_proxy_init_win.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_CHILD_DWRITE_FONT_PROXY_DWRITE_FONT_PROXY_INIT_WIN_H_
 #define CONTENT_CHILD_DWRITE_FONT_PROXY_DWRITE_FONT_PROXY_INIT_WIN_H_
 
 #include "base/callback.h"
 #include "content/common/content_export.h"
 #include "ipc/ipc_sender.h"
 
 namespace content {
 
-// Initializes the dwrite font proxy.
-CONTENT_EXPORT void InitializeDWriteFontProxy();
+// Initializes the dwrite font proxy, using the specified callback to obtain
+// the sender to be used for sending IPC messages to the browser process.
+CONTENT_EXPORT void InitializeDWriteFontProxy(
+    const base::Callback<IPC::Sender*(void)>& sender);
 
 // Uninitialize the dwrite font proxy. This is safe to call even if the proxy
 // has not been initialized. After this, calls to load fonts may fail.
 CONTENT_EXPORT void UninitializeDWriteFontProxy();
 
 // Configures the dwrite font proxy to use the specified sender. This can be
 // useful in tests which use a fake render thread which is unable to process
 // font IPC messages. This should only be called when running as a test.
 CONTENT_EXPORT void SetDWriteFontProxySenderForTesting(IPC::Sender* sender);
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_DWRITE_FONT_PROXY_DWRITE_FONT_PROXY_INIT_WIN_H_