Bug 1350759 Make unknown optional_permissions non-fatal r=kmag

MozReview-Commit-ID: 8IgV2i4b8Ot

--HG--
extra : rebase_source : 70eba84abdc10f7ac9736a0b26b3f10b10a85919

toolkit/components/extensions/schemas/manifest.json

@@ -181,7 +181,15 @@
 
           "optional_permissions": {
             "type": "array",
-            "items": { "$ref": "OptionalPermission" },
+            "items": {
+              "choices": [
+                { "$ref": "OptionalPermission" },
+                {
+                  "type": "string",
+                  "deprecated": "Unknown optional permission ${value}"
+                }
+              ]
+            },
             "optional": true,
             "default": []
           },