- Background Parsers cannot get the following data from Isolate (pass it to the
ctor instead): stack limit (background Parsers need a different stack limit),
UnicodeCache (background parsers need a separate UnicodeCache), hash seed
(Parser cannot access the Heap to get it). The Parser::Parse API won't change.

- Make the internalization phase (where Parser interacts with the heap) more
explicit. Previously, Parser was interacting with the heap here and there.

- Move HandleSourceURLComments out of DoParseProgram, so that background parsing
can use DoParseProgram too.

BUG=
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/527763002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23600 ce2b1a6d-e550-0410-aec6-3dcde31c8c00