media: Add string for enabling protected content

This CL only adds the string to enable protected content. The string is copied from https://chromiumcodereview.appspot.com/2679723003/ with modifications. Landing it first so it could be localized. The CL that uses it will come shortly.

NOTRY=true
NOPRESUBMIT=true
TBR=stevenjb@chromium.org
BUG=686430

Review-Url: https://codereview.chromium.org/2688433002
Cr-Commit-Position: refs/heads/master@{#448851}
1 file changed