Use C++11 range based iteration for invalidation sets.

Shortens down the source and improves readability.
Also removed a left-over include.

R=chrishtr@chromium.org

Review URL: https://codereview.chromium.org/633343002

git-svn-id: svn://svn.chromium.org/blink/trunk@183416 bbb929c8-8fbe-4397-9dbb-9b2b20218538