Parser: delay throwing errors.

Parser: delay throwing errors.

This makes Parser a bit more independent of Isolate during the recursive descent
phase. That is necessary for making it possible to run Parser on a non-main
thread in the future.

Proof of concept CL for the the "Parser independent of Isolate" work is here:
https://codereview.chromium.org/231073002/

BUG=
R=rossberg@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21385

[marja, 2014-05-20 09:04:59]

rossberg, ptal

This is an independent chunk split out of the "delay string internalization" WIP
you had a look at (thanks for comments for that one!)

[rossberg, 2014-05-20 12:19:00]

lgtm

[marja, 2014-05-20 12:22:14]

Committed patchset #1 manually as r21385 (presubmit successful).