(Pre)Parser: Simplify NewExpression handling.

Notes:
- We use simple recursion to keep track of how many "new" operators we have seen
  and where.
- This makes the self-baked stack class PositionStack in parser.cc unnecessary.
- Now the logic is also unified between Parser and PreParser.
- It might have been a copy-paste artifact (ParseLeftHandSideExpression ->
  ParseMemberWithNewPrefixesExpression) that the logic was so complicated
  before.

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

Review URL: https://codereview.chromium.org/166943002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19386 ce2b1a6d-e550-0410-aec6-3dcde31c8c00