test: Added smoke test for pageAction.show fallback to no callback on chrome.

test/fixtures/runtime-messaging-extension/background.js

@@ -5,6 +5,12 @@ console.log(name, "background page loaded");
 browser.runtime.onMessage.addListener((msg, sender) => {
   console.log(name, "background received msg", {msg, sender});
 
+  try {
+    browser.pageAction.show(sender.tab.id);
+  } catch (err) {
+    return Promise.resolve(`Unexpected error on pageAction.show: ${err}`);
+  }
+
   return Promise.resolve("background page reply");
 });
 

test/fixtures/runtime-messaging-extension/manifest.json

@@ -20,5 +20,8 @@
       "browser-polyfill.js",
       "background.js"
     ]
+  },
+  "page_action": {
+    "default_title": "a page action"
   }
 }