grokdump.py: work around int size limits on xrange
grokdump.py: work around int size limits on xrange

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1158933007

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28680}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh