Some uses use uint64_t instead of int64_t to avoid compiler warnings
about illegal narrowing of values with the MSB set.

R=tebbi@chromium.org,mlippautz@chromium.org

Bug: v8:7109
Change-Id: I6e861f48828bd931c451ef336672a260c13ae042
Reviewed-on: https://chromium-review.googlesource.com/803275
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49797}