Move media tests to their proper location.

These tests are actually media tests that happened to use Shadow DOM.
They should live with other media tests.

R=ojan
TBR=ojan
BUG=282087

Review URL: https://codereview.chromium.org/26521002

git-svn-id: svn://svn.chromium.org/blink/trunk@159128 bbb929c8-8fbe-4397-9dbb-9b2b20218538