Clamping the number of repetitions when using the repeat() function.

The ED suggests now to be able to clamp the number of repetitions when
using the repeat() function, taking precautions about excessive memory
usage.

BUG=79180

Review URL: https://codereview.chromium.org/251643002

git-svn-id: svn://svn.chromium.org/blink/trunk@173031 bbb929c8-8fbe-4397-9dbb-9b2b20218538