Don't copy the initiator during preload

When we wrote this code originally, the initiator strings weren't threadsafe so
we needed to make an isolated copy of them. Now they are threadsafe, so we can
just use them directly.

I got to this line of code by chasing down some unnecessary work on a profile
of mry1390.ir, but I doubt this change is measurable.

R=eseidel

Review URL: https://chromiumcodereview.appspot.com/22699004

git-svn-id: svn://svn.chromium.org/blink/trunk@155802 bbb929c8-8fbe-4397-9dbb-9b2b20218538