rustdoc-gui tests sporadically failing

[ehuss]

The src/test/rustdoc-gui tests have been sporadically failing on CI:

• Rollup of 7 pull requests #93778 (comment)
• Rollup of 7 pull requests #93778 (comment)
• Fix HashMap not displaying correctly in VS debugger #93626 (comment)
• Rollup of 8 pull requests #93677 (comment)
• rustdoc: Special-case macro lookups less #93721 (comment)'

These may have started with #93597
cc @GuillaumeGomez

There are various different errors:

/checkout/src/test/rustdoc-gui/search-tab-selection-if-current-is-empty.goml search-tab-selection-if-current-is-empty... FAILED
[ERROR] (line 6) TimeoutError: waiting for selector "#titles" failed: timeout 30000ms exceeded: for command `wait-for: "#titles"`

/checkout/src/test/rustdoc-gui/search-result-display.goml search-result-display... FAILED
[ERROR] (line 6) TimeoutError: waiting for selector "#titles" failed: timeout 30000ms exceeded: for command `wait-for: "#titles"`

/checkout/src/test/rustdoc-gui/src-font-size.goml An exception occured: read ECONNRESET
== STACKTRACE ==
Error
    at innerRunTestCode (/node-v14.4.0-linux-x64/lib/node_modules/browser-ui-test/src/index.js:468:16)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async main (/checkout/src/tools/rustdoc-gui/tester.js:226:13)

/checkout/src/test/rustdoc-gui/mobile.goml An exception occured: Failed to launch the browser process!
Inconsistency detected by ld.so: dl-tls.c: 493: _dl_allocate_tls_init: Assertion `listp->slotinfo[cnt].gen <= GL(dl_tls_generation)' failed!


TROUBLESHOOTING: https://github.com/puppeteer/puppeteer/blob/master/docs/troubleshooting.md
== STACKTRACE ==
Error
Error
    at innerRunTestCode (/node-v14.4.0-linux-x64/lib/node_modules/browser-ui-test/src/index.js:468:16)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)

[GuillaumeGomez]

That is concerning... If it happens too many times, let's revert it.

[GuillaumeGomez]

There is also #94417.

[nikic]

It looks like rustdoc-gui tests are now consistently failing with:

2022-03-09T18:18:21.7017663Z /checkout/src/test/rustdoc-gui/mobile.goml mobile... FAILED
2022-03-09T18:18:21.7018773Z [ERROR] (line 27) Error: Evaluation failed: assert didn't fail: for command compare-elements-position-near-false: ("#preferred-light-theme .setting-name", "#preferred-light-theme .choice", {"y": 16})

[GuillaumeGomez]

I'm checking locally.