Mark a layout test as flaky on Linux Release

This test:
virtual/threaded/fast/scroll-behavior/smooth-scroll/mousewheel-scroll-interrupted.html
is flaky under Release as well on Linux.

Please refer to the Chromium flakiness dashboard here:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=virtual%2Fthreaded%2Ffast%2Fscroll-behavior%2Fsmooth-scroll%2Fmousewheel-scroll-interrupted.html

TBR=ymalik@chromium.org

Review-Url: https://codereview.chromium.org/2156953003
Cr-Commit-Position: refs/heads/master@{#406129}
1 file changed