Sort camera device list to use front camera first

media/capture/video/video_capture_device_descriptor.h

Index: media/capture/video/video_capture_device_descriptor.h
diff --git a/media/capture/video/video_capture_device_descriptor.h b/media/capture/video/video_capture_device_descriptor.h
index 84ff841dbf4347b67cc29e1534f66bd6cf7c1c53..a850cb8fb0f1306245c806c8bc62e043868d5afa 100644
--- a/media/capture/video/video_capture_device_descriptor.h
+++ b/media/capture/video/video_capture_device_descriptor.h
@@ -67,6 +67,9 @@ struct CAPTURE_EXPORT VideoCaptureDeviceDescriptor {
     return (other.device_id == device_id) && (other.capture_api == capture_api);
   }
   bool operator<(const VideoCaptureDeviceDescriptor& other) const {
+    // Front camera first

[wuchengli, 2017/01/24 04:25:09]

We should prefer on-device cameras over external cameras. Front > back > none. 

[henryhsu, 2017/01/24 04:55:45]

Done.

+    if (facing < other.facing)
+      return true;
     if (device_id < other.device_id)
       return true;
     return capture_api < other.capture_api;