pkg/polymer/test/custom_event_test times out on Dartium

[peter-ahe-google]

FAILED: none-dartium-checked release_ia32 pkg/polymer/test/custom_event_test
Expected: Pass Crash
Actual: Timeout
CommandOutput[dartium]:

stdout:
message:
  Dom could not be fetched, since the test timed out.

stderr:
This test timed out. The delay until the test actually started was: 0:00:00.069876.

BrowserOutput while running the test (* EXPERIMENTAL *):
BrowserOutput.stdout:
  
BrowserOutput.stderr:
  

To retest, run: /mnt/data/b/build/slave/dartium-lucid64-inc-be/build/src/dart/tools/testing/bin/linux/dart /mnt/data/b/build/slave/dartium-lucid64-inc-be/build/src/dart/tools/testing/dart/http_server.dart -p 53679 -c 33182 --build-directory=/mnt/data/b/build/slave/dartium-lucid64-inc-be/build/src/out/Release --runtime=dartium

Command[dartium]: /mnt/data/b/build/slave/dartium-lucid64-inc-be/build/src/dart/tools/testing/bin/linux/dart tools/testing/dart/launch_browser.dart dartium http://127.0.0.1:53679/root_dart/pkg/polymer/test/custom_event_test.html?crossOriginPort=33182
Took 0:01:00.069801

Short reproduction command (experimental):
    python tools/test.py -rdartium -mrelease --checked -t60 pkg/polymer/test/custom_event_test

[peter-ahe-google]

Might be related to issue #15497.

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cc @mkustermann.
Added Area-Pkg label.

[mkustermann]

See reply on issue #15497. I think we should wait with investigating until somebody has looked at issue #15497.

[jmesserly]

likely fixed. i'm removing this from status file in https://codereview.chromium.org/307793002

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Added AssumedStale label.