PeerConnectionTest.java: make the test work for the bots' v4l2loopback.

- Make the test agnostic to the actual resolution used, since v4l2_file_player
  is playing a non-640x480 file (go/httfw)
- Teach DeviceInfoLinux::FillCapabilityMap() about I420 since that's what
  v4l2_file_player is feeding.

Requires https://gist.github.com/fischman/2e9a9b2efd2ad363ef82 be applied to the
v4l2loopback driver code.

BUG=1796
R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1891004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4422 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_capture/linux/device_info_linux.cc

@@ -294,6 +294,10 @@ int32_t DeviceInfoLinux::FillCapabilityMap(int fd)
                     {
                         cap->rawType = kVideoYUY2;
                     }
+                    else if (videoFormats[fmts] == V4L2_PIX_FMT_YUV420)
+                    {
+                        cap->rawType = kVideoI420;
+                    }
                     else if (videoFormats[fmts] == V4L2_PIX_FMT_MJPEG)
                     {
                         cap->rawType = kVideoMJPEG;