There are typically 3-4 test cases in each run of content_browsertests that fail at the first attempt and succeed at the second. All of these are test cases involving the real camera. These cases can easily be found by opening the stdio logs from content_browsertest runs, e.g. [1], and searching for the string "Expected". 

Example output from a failure:
[171/214] WebRtcImageCaptureSucceedsBrowserTest.GetPhotoCapabilities/0 (224 ms)
[ RUN      ] WebRtcImageCaptureSucceedsBrowserTest.GetPhotoCapabilities/2
Xlib:  extension "RANDR" missing on display ":9".
[5548:5585:0622/073344.655188:618324168:ERROR:devtools_http_handler.cc(804)] 
DevTools listening on 127.0.0.1:40176

../../content/browser/webrtc/webrtc_image_capture_browsertest.cc:168: Failure
Value of: RunImageCaptureTestCase("testCreateAndGetPhotoCapabilitiesSucceeds()")
  Actual: false
Expected: true
[  FAILED  ] WebRtcImageCaptureSucceedsBrowserTest.GetPhotoCapabilities/2, where GetParam() = (1-byte object <00>, 1-byte object <00>) (164 ms)


[1] https://build.chromium.org/p/chromium.webrtc/builders/Linux%20Tester/builds/30208/steps/content_browsertests/logs/stdio