Port r19800 (4402a23)

Original commit message:
- Merge LanguageMode and StrictModeFlag enums
- Make harmony-scoping depend only on strict mode
- Free some bits on the way
- Plus additional clean-up and renaming

BUG=

Review URL: https://codereview.chromium.org/195693002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19828 ce2b1a6d-e550-0410-aec6-3dcde31c8c00