Improve the growth strategy for Vectors with inline storage.

Deeper details are in the bug, but as a headline item, this reduces the number
of reallocs of Vector<T, i> (i != 0) during NTP load from 1070 to 515.

BUG=289040

Review URL: https://chromiumcodereview.appspot.com/23601026

git-svn-id: svn://svn.chromium.org/blink/trunk@157658 bbb929c8-8fbe-4397-9dbb-9b2b20218538