Reverted on the way to rolling out 154271, which broke
fast/text-autosizing/cluster-inline-grid-flex-box.html

Revert "AtomicString and StringBuilder should be bloat-free"

This reverts commit 8bda221ee48a2df9ed7d39925323a0d76713257d.

git-svn-id: svn://svn.chromium.org/blink/trunk@154285 bbb929c8-8fbe-4397-9dbb-9b2b20218538