Sheriff: Mark http/tests/devtools/sources/debugger-ui/reveal-execution-line.js as flaky

This test occasionally times out on Linux and Win bots.

Bug: 1145424
Change-Id: I448093d26d39167f2c2653b314d34b36d7ef1d09
Tbr: nhiroki@chromium.org
Notry: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518307Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823871}

third_party/blink/web_tests/TestExpectations

@@ -6238,3 +6238,5 @@ crbug.com/997202 [ Mac ] virtual/transform-interop/external/wpt/css/css-transfor
 
 # Sheriff 2020-11-04
 crbug.com/1144273 http/tests/devtools/sources/debugger-ui/continue-to-location-markers-in-top-level-function.js [ Pass Failure ]
+crbug.com/1145424 [ Linux ] http/tests/devtools/sources/debugger-ui/reveal-execution-line.js [ Pass Timeout ]
+crbug.com/1145424 [ Win ] http/tests/devtools/sources/debugger-ui/reveal-execution-line.js [ Pass Timeout ]