Restrict the externally_connectable manifest key to effectively a single origin

chrome/test/data/extensions/manifest_tests/externally_connectable_ids_and_matches.json

 {
   "name": "unit_tests --gtest_filter=ExternallyConnectableTest.IDsAndMatches",
   "version": "1",
   "manifest_version": 2,
   "externally_connectable": {
     "ids": [
       "abcdefghijklmnopabcdefghijklmnop",
       "ponmlkjihgfedcbaponmlkjihgfedcba"
     ],
     "matches": [
       "http://example.com/",
       "*://*.google.com/*",
-      "http://build.chromium.org/*"
+      "http://build.chromium.org/*",
+      "http://appspot.com/*",
+      "http://com/*",
+      "http://go/*",
+      "http://no.wildcard.path/"
     ]
   }
 }