[Mojo Video Capture] Hook up video capture service behind a feature flag

content/browser/renderer_host/media/video_capture_provider.h

Index: content/browser/renderer_host/media/video_capture_provider.h
diff --git a/content/browser/renderer_host/media/video_capture_provider.h b/content/browser/renderer_host/media/video_capture_provider.h
index f0b72bb33507b60b9a688c0ae1fdd1f3d52c0783..10135040df2585c75cc055ea7370d48cd103ea3c 100644
--- a/content/browser/renderer_host/media/video_capture_provider.h
+++ b/content/browser/renderer_host/media/video_capture_provider.h
@@ -68,8 +68,13 @@ class LaunchedVideoCaptureDevice
                                               base::OnceClosure done_cb) = 0;
 };
 
+// Note: GetDeviceInfosAsync is only relevant for devices with
+// MediaStreamType == MEDIA_DEVICE_VIDEO_CAPTURE, i.e. camera devices.
 class CONTENT_EXPORT VideoCaptureProvider {
  public:
+  using GetDeviceInfosCallback =
+      base::Callback<void(const std::vector<media::VideoCaptureDeviceInfo>&)>;
+
   virtual ~VideoCaptureProvider() {}
 
   virtual void Uninitialize() = 0;
@@ -77,9 +82,7 @@ class CONTENT_EXPORT VideoCaptureProvider {
   // The passed-in |result_callback| must guarantee that the called
   // instance stays alive until |result_callback| is invoked.
   virtual void GetDeviceInfosAsync(
-      const base::Callback<
-          void(const std::vector<media::VideoCaptureDeviceInfo>&)>&
-          result_callback) = 0;
+      const GetDeviceInfosCallback& result_callback) = 0;
 
   virtual std::unique_ptr<VideoCaptureDeviceLauncher>
   CreateDeviceLauncher() = 0;