rebaseline_server: force checksumValue to an integer to prevent spurious comparison failures

Without this change, SKP tests *appeared* to fail because the actuals reported
their checksumValues as integers, while the expectations recorded their
checksumValues as strings.

NOTREECHECKS=true
NOTRY=true
R=stephana@google.com
TBR=stephana
(SkipBuildbotRuns)

Author: epoger@google.com

Review URL: https://codereview.chromium.org/489023003
1 file changed