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 54 matching lines @@
   //
   // 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();
+
+  // Utility function useful for implementations
+  static std::string CreateRandomMediaDeviceIDSalt();

[jochen (gone - plz use gerrit), 2016/06/03 12:50:25]

as jam@ pointed out, you don't need to expose this method, embedders can just
call ResourceContext::GetMediaDeviceIDSalt()

[Guido Urdaneta, 2016/06/03 13:09:44]

The MediaDeviceIDSalt class uses that method to generate a random salt and store
it in preferences. This class does not know about ResourceContext, but it's used
by the profile implementation of ResourceContext.

If we don't expose it we need either to duplicate the method in
MediaDeviceIDSalt or do some less trivial refactoring in order to reuse the
ResourceContext method.
Since the utility method is almost a one-liner it's not such a big deal to
duplicate it. Are you OK with this?

+
+ private:
+  const std::string media_device_id_salt_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_