Update protocol.json to support explanations for securityStateChanged.
Update protocol.json to support explanations for securityStateChanged.

BUG=501551

Review URL: https://codereview.chromium.org/1195533002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@197393 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk