Add comments about lazy parsing and lazy compilation.

Also rename is_lazily_compiled in (Pre)Parser; it really means "is lazily
parsed" and doesn't correspond to the lazy compilation decision.

R=svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/169223009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19492 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Re-enable fast/js/reserved-words-as-property.html.

Error message migration is done and Blink has updated the expected result.

R=yangguo@chromium.org, ulan@chromium.org
BUG=v8:3126
LOG=N

Review URL: https://codereview.chromium.org/169353004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19493 ce2b1a6d-e550-0410-aec6-3dcde31c8c00