http/tests/devtools/tracing/worker-events.js
virtual/threaded/http/tests/devtools/tracing/worker-events.js
These two tests are failing very frequently on Mac10.13 (dbg), and sometimes on Linux/Win (dbg) and ASAN bot.

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=http%2Ftests%2Fdevtools%2Ftracing%2Fworker-events.js


This is the output when failing.
https://test-results.appspot.com/data/layout_results/Mac10_13_Tests__dbg_/3789/layout-test-results/results.html

Here is a copy from the results.html.
====
Tests that worker events are recorded with proper devtools metadata events.

error: TypeError: Cannot read property 'tracingBufferUsage' of null TypeError: Cannot read property 'tracingBufferUsage' of null
    at SDK.TracingManager._bufferUsage (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:4802:96)
    at SDK.TracingDispatcher.bufferUsage (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:4812:64)
    at Protocol.InspectorBackend._DispatcherPrototype.dispatch (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:3380:26)
    at SDK.Target._onMessage (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:3333:31)
    at SDK.MainConnection._dispatchMessage (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:3470:41)
    at Common.Object.dispatchEventToListeners (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:490:23)
    at innerDispatch (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:967:98)
    at Host.InspectorFrontendAPIImpl._dispatch (file:///b/s/w/ir/out/Debug/resources/inspector/shell.js:967:1)
    at DevToolsAPIImpl._dispatchOnInspectorFrontendAPI (chrome-devtools://devtools/bundled/devtools_compatibility.js:57:36)
    at DevToolsAPIImpl.dispatchMessage (chrome-devtools://devtools/bundled/devtools_compatibility.js:134:12)
Got DevTools worker metadata event(1): TracingSessionIdForWorker
Got DevTools worker metadata event(2): TracingSessionIdForWorker