Disable failing plugin tests on Linux after the switch to Aura.
BUG=125106
R=japhet@chromium.org

Review URL: https://codereview.chromium.org/137353005

git-svn-id: svn://svn.chromium.org/blink/trunk@165480 bbb929c8-8fbe-4397-9dbb-9b2b20218538