Bug 1494796 - wait in aboutdebugging addons nobg test for tabs before closing; r=jdescottes

This test was failing due to the tab closing before a response from the tab was recieved.
It is due to the threadClient closing more quickly. This waits for the last message before closing

Differential Revision: https://phabricator.services.mozilla.com/D32718

--HG--
extra : moz-landing-system : lando

devtools/client/aboutdebugging-new/test/browser/browser_aboutdebugging_addons_debug_nobg.js

@@ -23,6 +23,7 @@ const ADDON_NOBG_NAME = "test-devtools-webextension-nobg";
 add_task(async function testWebExtensionsToolboxNoBackgroundPage() {
   await enableExtensionDebugging();
   const { document, tab, window } = await openAboutDebugging();
+  const store = window.AboutDebugging.store;
   await selectThisFirefoxPage(document, window.AboutDebugging.store);
 
   await installTemporaryExtensionFromXPI({
@@ -37,8 +38,10 @@ add_task(async function testWebExtensionsToolboxNoBackgroundPage() {
   const toolbox = getToolbox(devtoolsWindow);
 
   const onToolboxClose = gDevTools.once("toolbox-destroyed");
-  toolboxTestScript(toolbox, devtoolsTab);
+  toolboxTestScript(toolbox, devtoolsTab, window);
 
+  // we need to wait for the tabs request to complete before continuing
+  await waitForDispatch(store, "REQUEST_TABS_SUCCESS");
   // The test script will not close the toolbox and will timeout if it fails, so reaching
   // this point in the test is enough to assume the test was successful.
   info("Wait for the toolbox to close");