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

media/video/capture/mac/video_capture_device_factory_mac_unittest.mm

 // 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.
 
 #include "base/command_line.h"
+#include "base/message_loop/message_loop_proxy.h"
 #include "media/base/media_switches.h"
 #import "media/video/capture/mac/avfoundation_glue.h"
 #include "media/video/capture/mac/video_capture_device_factory_mac.h"
 #include "media/video/capture/mac/video_capture_device_mac.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace media {
 
 class VideoCaptureDeviceFactoryMacTest : public testing::Test {
   virtual void SetUp() {
     CommandLine::ForCurrentProcess()->AppendSwitch(
         switches::kEnableAVFoundation);
   }
 };
 
 TEST_F(VideoCaptureDeviceFactoryMacTest, ListDevicesAVFoundation) {
   if (!AVFoundationGlue::IsAVFoundationSupported()) {
     DVLOG(1) << "AVFoundation not supported, skipping test.";
     return;
   }
-  VideoCaptureDeviceFactoryMac video_capture_device_factory;
+  VideoCaptureDeviceFactoryMac video_capture_device_factory(
+      base::MessageLoopProxy::current());
 
   VideoCaptureDevice::Names names;
   video_capture_device_factory.GetDeviceNames(&names);
   if (!names.size()) {
     DVLOG(1) << "No camera available. Exiting test.";
     return;
   }
   // There should be no blacklisted devices, i.e. QTKit.
   std::string device_vid;
   for (VideoCaptureDevice::Names::const_iterator it = names.begin();
       it != names.end(); ++it) {
     EXPECT_EQ(it->capture_api_type(), VideoCaptureDevice::Name::AVFOUNDATION);
   }
 }
 
 };  // namespace media