Rotate frames correctly for back camera

media/capture/video/linux/video_capture_device_linux.h

Index: media/capture/video/linux/video_capture_device_linux.h
diff --git a/media/capture/video/linux/video_capture_device_linux.h b/media/capture/video/linux/video_capture_device_linux.h
index e8adbde8df41715bdd075c0c921c3f6446eb4383..b8275063932a576dc07019e647c669a89d71c4c2 100644
--- a/media/capture/video/linux/video_capture_device_linux.h
+++ b/media/capture/video/linux/video_capture_device_linux.h
@@ -50,6 +50,9 @@ class VideoCaptureDeviceLinux : public VideoCaptureDevice {
  private:
   static int TranslatePowerLineFrequencyToV4L2(PowerLineFrequency frequency);
 
+  // Return true if the camera is back-facing.
+  bool GetCameraFacing(const VideoCaptureDeviceDescriptor& device_descriptor);
+
   // Internal delegate doing the actual capture setting, buffer allocation and
   // circulation with the V4L2 API. Created and deleted in the thread where
   // VideoCaptureDeviceLinux lives but otherwise operating on |v4l2_thread_|.
@@ -59,6 +62,8 @@ class VideoCaptureDeviceLinux : public VideoCaptureDevice {
 
   const VideoCaptureDeviceDescriptor device_descriptor_;
 
+  bool is_back_camera_;

[wuchengli, 2016/11/16 12:15:19]

I think we need three states -- back facing, front facing, and unknown (or
external).

[shenghao, 2016/11/17 08:41:44]

But what we really cares is whether it is a back camera. For external and front
camera, we don't need to adjust the rotation value.

[wuchengli, 2016/11/17 09:26:04]

OK. Let's document it then.
// True if the camera is world-facing. False if the camera is user-facing,
external, or unknown.

[shenghao, 2016/11/17 10:15:55]

Done.

+
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoCaptureDeviceLinux);
 };