Revert "Disable two flaky tests on ChromeOS"

This reverts commit fed7475d501d0622e3604313eb93867405cba55f.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Disable two flaky tests on ChromeOS
> 
> Disable ShelfLayoutManagerTest.FlingUpOnShelfForFullscreenAppList
> Disable WindowSelectorTest.RoundedEdgeMaskVisibility
> 
> Tbr: xiyuan, xdai
> Bug: 864467, 864465
> Change-Id: I77a0dbcddad5176575f0dc5991beb9eef8090167
> Reviewed-on: https://chromium-review.googlesource.com/1140683
> Reviewed-by: Owen Min <zmin@chromium.org>
> Commit-Queue: Owen Min <zmin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#575707}

TBR=zmin@chromium.org

Change-Id: I2aaceb5588030a1b14edf9b0c1d2da6165cbf8f1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 864467, 864465
Reviewed-on: https://chromium-review.googlesource.com/1140460
Reviewed-by: CJ DiMeglio <lethalantidote@chromium.org>
Commit-Queue: CJ DiMeglio <lethalantidote@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575865}
2 files changed