[autotest] Add a presubmit hook to validate commited json file

BUG=chromium:581852
TEST=local

Change-Id: Ib1b018f0a2765f0c66157fb2d9a7f4b13e4c2336
Reviewed-on: https://chromium-review.googlesource.com/324307
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Dan Shi <dshi@google.com>
2 files changed