The ParserTypes class has typedefs provided by the preparser or the
parser (e.g. PreParserExpression vs Expression*). Some of those typedefs
had gotten stale and were getting in the way, especially on gcc. We
also were making inconsistent use of aliases in parser-base.h; now their
use is much more consistent.

Review-Url: https://codereview.chromium.org/2305523002
Cr-Commit-Position: refs/heads/master@{#39101}