Add functionality to get default media device IDs from user preferences.

chrome/browser/ui/media_utils.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.
 
 #ifndef CHROME_BROWSER_UI_MEDIA_UTILS_H_
 #define CHROME_BROWSER_UI_MEDIA_UTILS_H_
 
 #include "base/callback.h"
 #include "content/public/common/media_stream_request.h"
 
 class GURL;
 class Profile;
 
 namespace content {
 class WebContents;
 }
 
 void RequestMediaAccessPermission(
     content::WebContents* web_contents,
     Profile* profile,
     const content::MediaStreamRequest& request,
     const content::MediaResponseCallback& callback);
 
 bool CheckMediaAccessPermission(content::WebContents* web_contents,
                                 const GURL& security_origin,
                                 content::MediaStreamType type);
 
+std::string GetDefaultMediaDeviceId(content::WebContents* web_contents,
+                                    content::MediaStreamType type);
+
 #endif  // CHROME_BROWSER_UI_MEDIA_UTILS_H_