Add MJPEG support to FakeVideoCaptureDevice

media/capture/video/fake_video_capture_device.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 MEDIA_CAPTURE_VIDEO_FAKE_VIDEO_CAPTURE_DEVICE_H_
 #define MEDIA_CAPTURE_VIDEO_FAKE_VIDEO_CAPTURE_DEVICE_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 
 #include "media/capture/video/video_capture_device.h"
 
 namespace media {
 
 // Encapsulates factory logic to make a working FakeVideoCaptureDevice based
 // on a given target OutputMode and frame rate.
 class CAPTURE_EXPORT FakeVideoCaptureDeviceMaker {
  public:
+  enum class PixelFormat { I420, Y16, MJPEG };
   enum class DeliveryMode {
     USE_DEVICE_INTERNAL_BUFFERS,
     USE_CLIENT_PROVIDED_BUFFERS
   };
 
   static void GetSupportedSizes(std::vector<gfx::Size>* supported_sizes);
 
+  static media::VideoPixelFormat TranslateToMediaVideoPixelFormat(
+      PixelFormat format);

[mcasas, 2017/02/22 20:26:33]

We already have a |VideoPixelFormat|. I think you want
to limit the ones accepted/supported by this particular
class (and by PacmanFramePainter, where we have 
another redefinition).  Find other way, e.g. DCHECKs,
otherwise the benefits of compile-time checking that
only supported formats are used, are overriden by the
extra code you need to translate back and forth.

[chfremer, 2017/02/23 01:14:28]

You are right. The reason I added these enum classes is as a C++ way to express
that only a certain subset of formats is supported. I feel that doing so is much
better than expressing the same using runtime checks and comments. I don't see
how the need to translate back and forth negates this.

In the new patch set, I am changing one direction of the translation from an
explicit mapping to a static_cast. Please let me know if that eases (or
increases?) the concern about the translation.

When you recommend trying to find a solution using DCHECKs, is there some
alternative you see that does not boil down to runtime checks and comments?

+
   static std::unique_ptr<VideoCaptureDevice> MakeInstance(
-      VideoPixelFormat pixel_format,
+      PixelFormat pixel_format,
       DeliveryMode delivery_mode,
       float frame_rate);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_FAKE_VIDEO_CAPTURE_DEVICE_H_