GitLab

Previously when test results presentation does not receive any json
input file, the script will raise a parser error. This is confusing to
developer, because they may mistake the parser error in this script as
the cause of the crash, instead of the reason why no json input file is
given at the first place.

In this cl, test results presentation will not raise error anymore when
no json file is given.

BUG=715972

Review-Url: https://codereview.chromium.org/2845973004
Cr-Commit-Position: refs/heads/master@{#467834}