Mark testCopyLinkTextSimple test as flaky

BUG=326769
TBR=aelias@chromium.org,aurimas@chromium.org,qsr@chromium.org

Review URL: https://codereview.chromium.org/109543002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239484 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239484