Add versioning to PluginFinder metadata.

chrome/browser/resources/plugin_metadata/plugins_mac.json

 {
+  "x-version": 1,
   "google-talk": {
     "mime_types": [
     ],
     "versions": [
       {
         "version": "0",
         "status": "up_to_date",
         "comment": "'Google Talk Plugin' and 'Google Talk Plugin Video Accelerator' use two completely different versioning schemes, so we can't define a minimum version."
       }
     ],
@@ skipping 255 matching lines @@
       {
         "version": "0",
         "status": "up_to_date",
         "comment": "Chrome PDF Viewer has no version information."
       }
     ],
     "name": "Chrome PDF Viewer",
     "group_name_matcher": "*Chrome PDF Viewer*"
   }
 }