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

chrome/browser/media/webrtc/media_capture_devices_dispatcher.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 CHROME_BROWSER_MEDIA_WEBRTC_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_
 #define CHROME_BROWSER_MEDIA_WEBRTC_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_
 
 #include <deque>
 #include <list>
 #include <map>
 #include <memory>
+#include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
 #include "base/memory/singleton.h"
 #include "base/observer_list.h"
 #include "content/public/browser/media_observer.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "content/public/common/media_stream_request.h"
 
@@ skipping 80 matching lines @@
   // Helper to get the default devices which can be used by the media request.
   // Uses the first available devices if the default devices are not available.
   // If the return list is empty, it means there is no available device on the
   // OS.
   // Called on the UI thread.
   void GetDefaultDevicesForProfile(Profile* profile,
                                    bool audio,
                                    bool video,
                                    content::MediaStreamDevices* devices);
 
+  // Helper to get default device IDs. If the returned value is an empty string,
+  // it means that there is no default device for the given device |type|. The
+  // only supported |type| values are content::MEDIA_DEVICE_AUDIO_CAPTURE and
+  // content::MEDIA_DEVICE_VIDEO_CAPTURE.
+  // Must be called on the UI thread.
+  std::string GetDefaultDeviceIdForProfile(Profile* profile,
+                                           content::MediaStreamType type);
+
   // Helpers for picking particular requested devices, identified by raw id.
   // If the device requested is not available it will return NULL.
   const content::MediaStreamDevice*
   GetRequestedAudioDevice(const std::string& requested_audio_device_id);
   const content::MediaStreamDevice*
   GetRequestedVideoDevice(const std::string& requested_video_device_id);
 
   // Returns the first available audio or video device, or NULL if no devices
   // are available.
   const content::MediaStreamDevice* GetFirstAvailableAudioDevice();
@@ skipping 75 matching lines @@
 
   std::unique_ptr<DesktopStreamsRegistry> desktop_streams_registry_;
 
   // Handlers for processing media access requests.
   ScopedVector<MediaAccessHandler> media_access_handlers_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaCaptureDevicesDispatcher);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_WEBRTC_MEDIA_CAPTURE_DEVICES_DISPATCHER_H_