Redo r19140 with better efficiency.

Redo r19140 with better efficiency.

Still relevant parts of the original commit message:

Unify paren handling in Parser and PreParser.

It is only needed in (Pre)Parser::ParseExpressionOrLabelledStatement for not
recognizing parenthesized identifiers as labels and in
(Pre)Parser::ParseSourceElements for not recognizing a parenthesized string as
directive prologue.

Parser Expressions don't keep track of whether they're parenthesized, so
PreParser Expressions shouldn't either.

BUG=3126
LOG=N
R=ulan@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=19153

[ulan, 2014-02-06 13:11:11]

lgtm

[marja, 2014-02-06 13:12:18]

Committed patchset #1 manually as r19153 (presubmit successful).