This CL fixes the first bug I found with the new fuzzing. The problem is
that the number of locals is unbounded. This CL bounds the number of
locals of one type with 8000000, an arbitrary number.

R=titzer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2271803004
Cr-Commit-Position: refs/heads/master@{#38936}