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=yangguo@chromium.org

Bug: v8:6837, v8:6921
Change-Id: I0c2deaea3f2ff5b5b25ba658470850534f1900ac
Reviewed-on: https://chromium-review.googlesource.com/681435
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48594}