Store first and last newline position in the token text for string literals and comments.

Store first and last newline position in the token text for string literals and comments.

Summary:
Store first and last newline position in the token text for string literals and
comments to avoid doing .find('\n') for each possible solution.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek
Differential Revision: http://llvm-reviews.chandlerc.com/D1556

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189758 91177308-0d34-0410-b5e6-96231b3b80d8