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

media/video/capture/file_video_capture_device_factory.cc

Index: media/video/capture/file_video_capture_device_factory.cc
diff --git a/media/video/capture/file_video_capture_device_factory.cc b/media/video/capture/file_video_capture_device_factory.cc
index 772f4f61c57aee942d2f9baee6d918d661405cc2..ae7845064e958f1d8bf40bc2fa73407e49863a37 100644
--- a/media/video/capture/file_video_capture_device_factory.cc
+++ b/media/video/capture/file_video_capture_device_factory.cc
@@ -25,8 +25,8 @@ base::FilePath GetFilePathFromCommandLine() {
 }
 
 scoped_ptr<VideoCaptureDevice> FileVideoCaptureDeviceFactory::Create(
-    scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner,
     const VideoCaptureDevice::Name& device_name) {
+  DCHECK(thread_checker_.CalledOnValidThread());
 #if defined(OS_WIN)
   return scoped_ptr<VideoCaptureDevice>(new FileVideoCaptureDevice(
       base::FilePath(base::SysUTF8ToWide(device_name.name()))));
@@ -38,6 +38,7 @@ scoped_ptr<VideoCaptureDevice> FileVideoCaptureDeviceFactory::Create(
 
 void FileVideoCaptureDeviceFactory::GetDeviceNames(
     VideoCaptureDevice::Names* const device_names) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(device_names->empty());
   base::FilePath command_line_file_path = GetFilePathFromCommandLine();
 #if defined(OS_WIN)
@@ -54,6 +55,7 @@ void FileVideoCaptureDeviceFactory::GetDeviceNames(
 void FileVideoCaptureDeviceFactory::GetDeviceSupportedFormats(
     const VideoCaptureDevice::Name& device,
     VideoCaptureFormats* supported_formats) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   base::File file =
       FileVideoCaptureDevice::OpenFileForRead(GetFilePathFromCommandLine());
   VideoCaptureFormat capture_format;