Allow retrieval of media device ID salt even after ResourceContext has gone away.

content/public/browser/media_device_id.h

 // Copyright 2013 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.
 //
 // Media device IDs come in two flavors: The machine-wide unique ID of
 // the device, which is what we use on the browser side, and one-way
 // hashes over the unique ID and a security origin, which we provide
 // to code on the renderer side as per-security-origin IDs.
 
 #ifndef CONTENT_PUBLIC_BROWSER_MEDIA_DEVICE_ID_H_
 #define CONTENT_PUBLIC_BROWSER_MEDIA_DEVICE_ID_H_
 
 #include <string>
 
 #include "content/common/content_export.h"
+#include "content/public/browser/resource_context.h"
 #include "url/gurl.h"
 
 namespace content {
 
-class ResourceContext;
-
 // Generates a one-way hash of a device's unique ID usable by one
 // particular security origin.
 CONTENT_EXPORT std::string GetHMACForMediaDeviceID(
-    ResourceContext* rc,
+    const ResourceContext::SaltCallback& sc,
     const GURL& security_origin,
     const std::string& raw_unique_id);
 
 // Convenience method to check if |device_guid| is an HMAC of
 // |raw_device_id| for |security_origin|.
 CONTENT_EXPORT bool DoesMediaDeviceIDMatchHMAC(
-    ResourceContext* rc,
+    const ResourceContext::SaltCallback& sc,
     const GURL& security_origin,
     const std::string& device_guid,
     const std::string& raw_unique_id);
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_MEDIA_DEVICE_ID_H_