This patch removes the explicit classifier parameters from all
parsing methods and makes expression classifiers implicit in
the (pre)parser's implementation.  In this way, the implementation
is simplified and a proper stack of classifiers is enforced.

R=adamk@chromium.org,littledan@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2289663002
Cr-Commit-Position: refs/heads/master@{#39068}