Remove Vector reallocation code.

Replace the only usage with a simpler, faster optimization.
(The optimization isn't huge, it only triggers 5 times during NTP load.)

Review URL: https://chromiumcodereview.appspot.com/23475056

git-svn-id: svn://svn.chromium.org/blink/trunk@158003 bbb929c8-8fbe-4397-9dbb-9b2b20218538