Bug 1397098 - Wait for the content pref update after changing zoom level. r=adw

browser/base/content/test/tabs/browser.ini

@@ -28,7 +28,6 @@ skip-if = !e10s # Pref and test only relevant for e10s.
 [browser_pinnedTabs_closeByKeyboard.js]
 [browser_positional_attributes.js]
 [browser_preloadedBrowser_zoom.js]
-skip-if = !debug && (os == 'win' && (os_version == '6.1')) # Bug 1397098
 [browser_reload_deleted_file.js]
 skip-if = (debug && os == 'mac') || (debug && os == 'linux' && bits == 64) #Bug 1421183, disabled on Linux/OSX for leaked windows
 [browser_tabswitch_updatecommands.js]

browser/base/content/test/tabs/browser_preloadedBrowser_zoom.js

@@ -38,6 +38,21 @@ async function zoomNewTab(changeZoom, message) {
   const level = tab.linkedBrowser.fullZoom;
   BrowserTestUtils.removeTab(tab);
 
+  // Wait for the the update of the full-zoom content pref value, that happens
+  // asynchronously after changing the zoom level.
+  let cps2 = Cc["@mozilla.org/content-pref/service;1"].
+      getService(Ci.nsIContentPrefService2);
+  await BrowserTestUtils.waitForCondition(() => {
+    return new Promise(resolve => {
+      cps2.getByDomainAndName("about:newtab", "browser.content.full-zoom", null, {
+        handleResult(pref) {
+          resolve(level == pref.value);
+        },
+        handleCompletion() {},
+      });
+    });
+  });
+
   await checkPreloadedZoom(level, `${message}: ${level}`);
 }