Revert of Make default media device ID salts random by default

content/public/browser/resource_context.h

 // Copyright (c) 2012 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_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_
 #define CONTENT_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 36 matching lines @@
 
   // Create a platform KeygenHandler and pass it to |callback|. The |callback|
   // may be run synchronously.
   virtual void CreateKeygenHandler(
       uint32_t key_size_in_bits,
       const std::string& challenge_string,
       const GURL& url,
       const base::Callback<void(std::unique_ptr<net::KeygenHandler>)>&
           callback);
 
-  // Returns a random salt string that is used for creating media device IDs.
-  // Returns a random string by default.
-  virtual std::string GetMediaDeviceIDSalt();
-
-  // Utility function useful for embedders. Only needs to be called if
-  // 1) The embedder needs to use a new salt, and
-  // 2) The embedder saves its salt across restarts.
-  static std::string CreateRandomMediaDeviceIDSalt();
-
- private:
-  const std::string media_device_id_salt_;
+  // Returns a callback that can be invoked to get a random salt
+  // string that is used for creating media device IDs.  The salt
+  // should be stored in the current user profile and should be reset
+  // if cookies are cleared. The default is an empty string.
+  //
+  // It is safe to hold on to the callback returned and use it without
+  // regard to the lifetime of ResourceContext, although in general
+  // you should not use it long after the profile has been destroyed.
+  //
+  // TODO(joi): We don't think it should be unnecessary to use this
+  // after ResourceContext goes away. There is likely an underying bug
+  // in the lifetime of ProfileIOData vs. ResourceProcessHost, where
+  // sometimes ProfileIOData has gone away before RPH has finished
+  // being torn down (on the IO thread). The current interface that
+  // allows using the salt object after ResourceContext has gone away
+  // was put in place to fix http://crbug.com/341211 but I intend to
+  // try to figure out how the lifetime should be fixed properly. The
+  // original interface was just a method that returns a string.
+  //
+  // TODO(perkj): Make this method pure virtual when crbug/315022 is
+  // fixed.
+  typedef base::Callback<std::string()> SaltCallback;
+  virtual SaltCallback GetMediaDeviceIDSalt();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_