Enable video.WebRTC* tast tests on chrome bots.

video.WebRTC* tasts tests are disabled on chrome bot by CL:1363805
because of a bug reported at crbug.com/909975.
Since this bug was fixed by CL:1367388, we can run these tests now.

Bug: 909975
Change-Id: I74b719988470552fe5abc39f217dda0086e15e71
Reviewed-on: https://chromium-review.googlesource.com/c/1367333
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615910}

chromeos/BUILD.gn

@@ -431,10 +431,6 @@ if (is_cros_chrome_sdk) {
     disabled_tests = [
       # Disabled due to flake. https://crbug.com/909736
       "ui.MashLogin",
-
-      # Disabled due to DCHECK failures. https://crbug.com/909975
-      "video.WebRTCCamera",
-      "video.WebRTCPeerConnCameraVP8",
     ]
     tast_conditional = "!disabled && !\"group:*\" && !informational" +
                        " && (\"dep:chrome\" || \"dep:chrome_login\")"