Revert of Mark link-rel-prefetch-and-subresource flaky (patchset #1 of https://codereview.chromium.org/431153003/)

Reason for revert:
Bug fixed.

Original issue's description:
> Mark link-rel-prefetch-and-subresource flaky
> 
> TBR=alancutter@chromium.org
> NOTRY=true
> BUG=399459
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179348

Review URL: https://codereview.chromium.org/480083002

git-svn-id: svn://svn.chromium.org/blink/trunk@180481 bbb929c8-8fbe-4397-9dbb-9b2b20218538