Mark http/tests/devtools/tracing/timeline-script-parse.js as flaky on Linux

TBR=alph@chromium.org

Bug: 959129
Change-Id: I90a383f3ee617f58614b14f0d54675ffc612b703
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1604266Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658506}

third_party/blink/web_tests/TestExpectations

@@ -5967,7 +5967,7 @@ crbug.com/959002 crbug.com/959042 http/tests/devtools/elements/styles-4/undo-add
 
 # Sheriff 2019-05-06
 crbug.com/959372 [ Win ] external/wpt/import-maps/fallback.sub.tentative.html [ Pass Timeout ]
-crbug.com/959129 [ Win ] http/tests/devtools/tracing/timeline-script-parse.js [ Pass Failure ]
+crbug.com/959129 [ Win Linux ] http/tests/devtools/tracing/timeline-script-parse.js [ Pass Failure ]
 
 # Sheriff 2019-05-07
 crbug.com/960443 [ Mac10.10 Mac10.11 ] external/wpt/animation-worklet/worklet-animation-with-scroll-timeline.https.html [ Failure Pass ]