Use the (D)CHECK_{EQ,NE,GT,...} macros instead of (D)CHECK with an
embedded comparison. This gives better error messages and also does the
right comparison for signed/unsigned mismatches.

This will allow us to reenable the readability/check cpplint check.

R=jgruber@chromium.org

Bug: v8:6837
Change-Id: I9c489ac0e1b15fd4789c37fd32c9d3c76121a288
Reviewed-on: https://chromium-review.googlesource.com/671343
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48079}