Add a flag to store perf results as a JSON file in the format specified by https://github.com/catapult-project/catapult/blob/master/dashboard/docs/data-format.md Bug: webrtc:7156 Change-Id: Ia5b0317f0f5dc8767fa219f42bc39bf4073203e8 Reviewed-on: https://webrtc-review.googlesource.com/29160 Reviewed-by: Patrik Höglund <phoglund@webrtc.org> Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org> Cr-Commit-Position: refs/heads/master@{#21082}