VideoCaptureDeviceFactory: Change device enumeration to callback + QTKit enumerates in UI thread.

media/video/capture/mac/video_capture_device_factory_mac.h

 // Copyright 2014 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.
 
 // Implementation of a VideoCaptureDeviceFactory class for Mac.
 
 #ifndef MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_DEVICE_FACTORY_MAC_H_
 #define MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_DEVICE_FACTORY_MAC_H_
 
 #include "media/video/capture/video_capture_device_factory.h"
 
 namespace media {
 
 // Extension of VideoCaptureDeviceFactory to create and manipulate Mac devices.
 class MEDIA_EXPORT VideoCaptureDeviceFactoryMac :
     public VideoCaptureDeviceFactory {
  public:
-  VideoCaptureDeviceFactoryMac();
-  virtual ~VideoCaptureDeviceFactoryMac() {}
+  static bool PlatformSupportsAVFoundation();
+
+  explicit VideoCaptureDeviceFactoryMac(
+      scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
+  virtual ~VideoCaptureDeviceFactoryMac();
 
   virtual scoped_ptr<VideoCaptureDevice> Create(
-      scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner,
       const VideoCaptureDevice::Name& device_name) OVERRIDE;
   virtual void GetDeviceNames(VideoCaptureDevice::Names* device_names) OVERRIDE;
+  virtual void EnumerateDeviceNames(const base::Callback<
+      void(scoped_ptr<media::VideoCaptureDevice::Names>)>& callback) OVERRIDE;
   virtual void GetDeviceSupportedFormats(
       const VideoCaptureDevice::Name& device,
       VideoCaptureFormats* supported_formats) OVERRIDE;
 
  private:
+  // Cache of |ui_task_runner| for enumerating devices there for QTKit.
+  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureDeviceFactoryMac);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_DEVICE_FACTORY_MAC_H_