Bug 1398974: Part 5 - Add content script to webext talos add-on. r=mixedpuppy,jmaher

MozReview-Commit-ID: DDPOrJ2nuhE

--HG--
extra : rebase_source : cf8397698356fb56172e8fcfefebd1a7065f58ce

testing/talos/talos/webextensions/dummy/manifest.json

@@ -15,6 +15,12 @@
     "webRequestBlocking"
   ],
   "background": {"scripts": ["background.js"]},
+  "content_scripts": [
+    {
+      "matches": ["<all_urls>"],
+      "js": ["content.js"]
+    }
+  ],
   "browser_action": {},
   "page_action": {}
 }