|SingleThreadProxy::SetRenderFrameObserver(...)| seems to be added recently in a2ff4f82109df55045dee9f54985a98054f86dc4.

jonross@ Can you help triage if the flaky is expected? Thanks!

```
22:11:53.117 5622 Retrying 1 unexpected failure, attempt 2 of 3...
22:11:53.117 5622 Sharding tests ...
22:11:53.117 5622 Starting 1 worker ...
22:11:53.118 5622 worker/0 starting
22:12:00.940 5622 killed pid 516
22:12:00.942 5622 worker/0 virtual/outofblink-cors/external/wpt/fetch/api/redirect/redirect-location-worker.html output stderr lines:
22:12:00.942 5622   Fontconfig warning: "/etc/fonts/fonts.conf", line 146: blank doesn't take any effect anymore. please remove it from your fonts.conf
22:12:00.943 5622   [1:1:0218/221155.032391:ERROR:single_thread_proxy.cc(648)] Not implemented reached in virtual void cc::SingleThreadProxy::SetRenderFrameObserver(std::unique_ptr<RenderFrameMetadataObserver>)
22:12:00.944 5622 [1/1] virtual/outofblink-cors/external/wpt/fetch/api/redirect/redirect-location-worker.html failed unexpectedly (test timed out)
22:12:00.944 5622 worker/0 killing primary driver
22:12:00.944 5622 worker/0 killing secondary driver
22:12:00.944 5622 worker/0 virtual/outofblink-cors/external/wpt/fetch/api/redirect/redirect-location-worker.html failed:
22:12:00.944 5622 worker/0  test timed out
22:12:00.944 5622 worker/0 killing secondary driver
22:12:00.944 5622 worker/0 exiting
22:12:00.944 5622 worker/0 cleaning up
22:12:00.944 5622 worker/0 killing primary driver
22:12:00.944 5622 worker/0 killing secondary driver
```

+mkwst@ who wrote the flaking test.

According to /third_party/WebKit/LayoutTests/FlagExpectations/site-per-process this test is expected to have Timeouts, which the logs in #1 cite.

The NOTIMPLEMENTED is currently expected, and will be gone soon. It would not cause a timeout.

Detected 16 new flakes for test/step "virtual/outofblink-cors/external/wpt/fetch/api/redirect/redirect-location-worker.html". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyYAsSBUZsYWtlIlV2aXJ0dWFsL291dG9mYmxpbmstY29ycy9leHRlcm5hbC93cHQvZmV0Y2gvYXBpL3JlZGlyZWN0L3JlZGlyZWN0LWxvY2F0aW9uLXdvcmtlci5odG1sDA. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

This bug and related Issue 730902 haven't seen any substantial update since last June when they were filed. I just hit this flake in my unrelated CL https://ci.chromium.org/buildbot/tryserver.chromium.linux/linux_chromium_rel_ng/651118 and am marking this test as flakily timing out both in the virtual/outofblink-cors virtual test suite as well as in its default mode.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f18e2e2b45614ba62ca3ad42ca083d78b9780b59

commit f18e2e2b45614ba62ca3ad42ca083d78b9780b59
Author: Kenneth Russell <kbr@chromium.org>
Date: Wed Feb 21 05:39:54 2018

Suppress redirect-location-worker.html flaky timeouts.

Since no action has been taken on these timeouts, suppressing
external/wpt/fetch/api/redirect/redirect-location-worker.html in its
default mode as well as in the virtual/outofblink-cors virtual test
suite.

TBR=mkwst@chromium.org

Bug: 730902, 813694
Change-Id: Ibd761efec9733eebcf8fc7948cfe0382208aa158
Reviewed-on: https://chromium-review.googlesource.com/927923
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538026}
[modify] https://crrev.com/f18e2e2b45614ba62ca3ad42ca083d78b9780b59/third_party/WebKit/LayoutTests/TestExpectations

The last of these flakes was from before I landed a patch to remove the suspected offending NOTIMPLEMENTED. (https://chromium-review.googlesource.com/c/chromium/src/+/926561)

The other flaking tests also suspected of this have stopped flaking.

mkwst@ you can re-enable the timeouts if you feel that is appropriate.

Removing Sheriff-Chromium since the flakiness should have stopped.