This converts existing "preparser" tests that expect a certain exception
message to be produced into "message" tests. Thereby we get much better
coverage because the former test suite degraded by now to just check
whether each test case threw or not, the exception message was not being
checked at all.

This also deprecates the ability of "preparser" to specify that single
test cases based on JS files are expected to throw, "messages" is far
superior, use that test suite instead.

R=machenbach@chromium.org
TEST=message,preparser

Review URL: https://codereview.chromium.org/1784013003

Cr-Commit-Position: refs/heads/master@{#34713}