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=jarin@chromium.org

Bug: v8:6837
Change-Id: I712580c2a4326e06ee3d6d0eb4ff8c7d24f5fdb9
Reviewed-on: https://chromium-review.googlesource.com/671227
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48135}