Pushed the detection logic down to ParseAndClassifyIdentifier in
preparation to having patterns in parameter positions.

R=arv@chromium.org,rossberg@chromium.org,wingo@igalia.com
BUG=v8:811
LOG=N

Review URL: https://codereview.chromium.org/1170153003

Cr-Commit-Position: refs/heads/master@{#28876}