Traitify ParserBase and move functions there.

Traitify ParserBase and move functions there.

(Second try, with fixes. First try: https://codereview.chromium.org/149913006/ )

The long-term goal is to move all recursive descent functions from Parser and
PreParser into ParserBase, but first they need to be unified.

Notes:
- The functions moved in this CL: ParseIdentifier, ParseIdentifierName,
ParseIdentifierNameOrGetOrSet, ParseIdentifierOrStrictReservedWord.
- IOW, this CL removes Parser::ParseIdentifier and PreParser::ParseIdentifier
and adds ParserBase::ParseIdentifier, etc.
- Error reporting used to require virtual funcs; now error reporting is moved to
the Traits too, and ParserBase no longer needs to be virtual.
- I had to move PreParser::Identifier out of the PreParser class, because
otherwise PreParserTraits cannot use it in a typedef.

BUG=v8:3126
LOG=N
R=mstarzinger@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=19265

[Michael Starzinger, 2014-02-10 17:35:12]

LGTM (rubber-stamped).

[marja, 2014-02-11 09:35:41]

Committed patchset #1 manually as r19265 (presubmit successful).