Bug 1580826 - Ensure awaiting on fetchManifest before closing tab, r=yulia

Intermittent devtools/client/application/test/browser/browser_application_panel_sidebar.js | A promise chain failed to handle a rejection: Connection closed, pending request to server0.conn2.child1/manifestActor19, type fetchCanonicalManifest failed

Differential Revision: https://phabricator.services.mozilla.com/D46001

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

devtools/client/application/test/browser/browser_application_panel_sidebar.js

@@ -11,7 +11,7 @@ add_task(async function() {
   info("Test that we are displaying correctly the sidebar");
 
   await enableApplicationPanel();
-  const { panel, tab } = await openNewTabAndApplicationPanel();
+  const { panel, tab, target } = await openNewTabAndApplicationPanel();
   const doc = panel.panelWin.document;
 
   info("Waiting for the sidebar to be displayed");
@@ -23,6 +23,7 @@ add_task(async function() {
 
   // close the tab
   info("Closing the tab.");
+  await target.client.waitForRequestsToSettle();
   await BrowserTestUtils.removeTab(tab);
 });
 
@@ -48,6 +49,7 @@ add_task(async function() {
 
   // close the tab
   info("Closing the tab.");
+  await target.client.waitForRequestsToSettle();
   await BrowserTestUtils.removeTab(tab);
 });
 
@@ -58,7 +60,7 @@ add_task(async function() {
   const url = URL_ROOT + "resources/manifest/load-ok.html";
 
   await enableApplicationPanel();
-  const { panel, tab } = await openNewTabAndApplicationPanel(url);
+  const { panel, tab, target } = await openNewTabAndApplicationPanel(url);
   const doc = panel.panelWin.document;
 
   selectPage(panel, "manifest");
@@ -76,5 +78,6 @@ add_task(async function() {
 
   // close the tab
   info("Closing the tab.");
+  await target.client.waitForRequestsToSettle();
   await BrowserTestUtils.removeTab(tab);
 });