Tidy up Vector destruction in a way that doesn't cause a Mac perf regression.

Reland of
https://codereview.chromium.org/23531010
and
https://chromiumcodereview.appspot.com/23455034

BUG=289080,288468
R=abarth@chromium.org, tsepez@chromium.org

Review URL: https://codereview.chromium.org/23567028

git-svn-id: svn://svn.chromium.org/blink/trunk@157740 bbb929c8-8fbe-4397-9dbb-9b2b20218538