Allow PeerConnection-createAnswer WPTs to fail

https://webrtc-review.googlesource.com/c/src/+/41042 will change
an error message in CreateAnswer which would break this WPT. Once
the WebRTC CL has rolled in the test expectation will be updated
and the test re-enabled.

Bug: 806005
Change-Id: I53855be0dcc23bb76a6a6087761198beb82262dc
Reviewed-on: https://chromium-review.googlesource.com/887371Reviewed-by: Henrik Boström <hbos@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Steve Anton <steveanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532041}

third_party/WebKit/LayoutTests/TestExpectations

@@ -1455,6 +1455,9 @@ crbug.com/769885 [ Linux ] virtual/android/fullscreen/full-screen-frameset.html
 crbug.com/492511 [ Mac ] fast/text/atsui-negative-spacing-features.html [ Failure ]
 crbug.com/492511 [ Mac ] fast/text/international/arabic-justify.html [ Failure ]
 
+# Tests that will start failing after this WebRTC CL is rolled in: https://webrtc-review.googlesource.com/c/src/+/41042
+crbug.com/806005 external/wpt/webrtc/RTCPeerConnection-createAnswer.html [ Pass Failure ]
+
 # Ref tests that fail due to differences in inline box structure, even though they contain the same text.
 # This happens because inline box layout uses fixed-point measurements, which can cause rounding differences.
 crbug.com/321237 [ Mac ] fast/selectors/007a.html [ Failure ]