Revert "Don't copy the initiator during preload"

This reverts commit r155802 due to a ~50% perf regression on parsert/html-parser.
See graphs here: https://chromeperf.appspot.com/report?masters=ChromiumWebkit&bots=chromium-rel-linux-webkit%2Cchromium-rel-mac6-webkit%2Cchromium-rel-win7-webkit&tests=blink_perf%2FParser_html-parser&checked=core

BUG=273219
TBR=abarth

Review URL: https://chromiumcodereview.appspot.com/23007016

git-svn-id: svn://svn.chromium.org/blink/trunk@156124 bbb929c8-8fbe-4397-9dbb-9b2b20218538