Remove obsolete distributed:: in layout tests

Did s/distributed::/content::/g.
They are in <title> etc., and no functional change in tests.

BUG=none
TEST=run affected layout tests

Review URL: https://codereview.chromium.org/286763002

git-svn-id: svn://svn.chromium.org/blink/trunk@174025 bbb929c8-8fbe-4397-9dbb-9b2b20218538