Follow-on to "Restore in-memory parser cache for V8 compile"
(rrev.com/528013002).

Fixes for review comments not handled in the original CL.

BUG=399580
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/549533002

git-svn-id: svn://svn.chromium.org/blink/trunk@181554 bbb929c8-8fbe-4397-9dbb-9b2b20218538