1) In ParseLazy, we're already using the heap, so we can also tell
AstValueFactory to internalize immediately. This is more efficient.

2) No need to collect the values in values_ and strings_ if they're already
internalized.

3) No need to collect AstValues which are strings in values_ since they don't
need to be internalized (the underlying strings will be internalized
separately).

BUG=429168
LOG=N
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/693803004

Cr-Commit-Position: refs/heads/master@{#25109}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25109 ce2b1a6d-e550-0410-aec6-3dcde31c8c00