Catch IOError when reading chartjson results in test_runner.py
Right now, if the results aren't there, the entire sharded perf tests step fails. This doesn't fix the underlying issue, but at least allows the rest of the tests to run and makes it clearer which step failed.
With Patch: http://simonhatch0.mon.corp.google.com:8013/builders/Android%20Nexus7v2%20Perf/builds/593
Without: http://simonhatch0.mon.corp.google.com:8013/builders/Android%20Nexus7v2%20Perf/builds/591
BUG=498412
Review URL: https://codereview.chromium.org/
1176613002
Cr-Commit-Position: refs/heads/master@{#333593}