Do not rotate frames from external cameras

media/capture/video/linux/video_capture_device_chromeos.cc

 // 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 "media/capture/video/linux/video_capture_device_chromeos.h"
 
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/macros.h"
@@ skipping 134 matching lines @@
     // |         ********    |
     // |      ****   *       |
     // |    ***      *       |
     // |    ***      *       |
     // |      ****   *       |
     // |         ********    |
     // -----------------------
     //
     // Therefore, for back camera, we need to rotate (360 - |rotation|).
     rotation = (360 - rotation) % 360;
+  } else if (lens_facing_ == VideoFacingMode::MEDIA_VIDEO_FACING_NONE) {
+    // External cameras have lens_facing as MEDIA_VIDEO_FACING_NONE.
+    // We don't want to rotate the frame even if the device rotates.
+    rotation = 0;

[chfremer, 2017/03/20 16:32:47]

As a drive-by nit, I wonder if we could make things more obvious by introducing
a member |rotates_with_device_| and setting it to false for external cameras.
Otherwise, we run the risk that future developers may not be aware that setting
a MEDIA_VIDEO_FACING_NONE implies no rotation with the device.

[shenghao, 2017/03/21 06:06:31]

Done.

   }
-  // Take into account camera orientation w.r.t. the display.
+  // Take into account camera orientation w.r.t. the display. External cameras
+  // would have camera_orientation_ as 0.
   rotation = (rotation + camera_orientation_) % 360;
   VideoCaptureDeviceLinux::SetRotation(rotation);
 }
 
 void VideoCaptureDeviceChromeOS::SetDisplayRotation(
     const display::Display& display) {
   if (display.IsInternal())
     SetRotation(display.rotation() * 90);
 }
 
 }  // namespace media