Make checkdeps.py correctly signal failure when using --json.

This is a followup to https://codereview.chromium.org/75693002/

TBR=joi
BUG=317931

Review URL: https://codereview.chromium.org/75793003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235865 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235865
Add missing comma to gypi file. BUG= TBR=scottmg316709

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235866 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235866