Bug 332195 - part 5: fix test for e10s, r=mconley

--HG--
extra : commitid : 5Cb58g4sU6s
extra : rebase_source : e22ceac2b58b2ad62587c7db0e7e8bc90565da72

browser/base/content/test/general/browser_openPromptInBackgroundTab.js

@@ -19,8 +19,11 @@ add_task(function*() {
   let firstTab = gBrowser.selectedTab;
   // load page that opens prompt when page is hidden
   let openedTab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, pageWithAlert, true);
+  let openedTabGotAttentionPromise = BrowserTestUtils.waitForAttribute("attention", openedTab, "true");
   // switch away from that tab again - this triggers the alert.
   yield BrowserTestUtils.switchTab(gBrowser, firstTab);
+  // ... but that's async on e10s...
+  yield openedTabGotAttentionPromise;
   // check for attention attribute
   is(openedTab.getAttribute("attention"), "true", "Tab with alert should have 'attention' attribute.");
   ok(!openedTab.selected, "Tab with alert should not be selected");
@@ -43,8 +46,15 @@ add_task(function*() {
   let ps = Services.perms;
   is(ps.ALLOW_ACTION, ps.testPermission(makeURI(pageWithAlert), "focus-tab-by-prompt"),
      "Tab switching should now be allowed");
+
+  let openedTabSelectedPromise = BrowserTestUtils.waitForAttribute("selected", openedTab, "true");
   // switch to other tab again
   yield BrowserTestUtils.switchTab(gBrowser, firstTab);
+
+  // This is sync in non-e10s, but in e10s we need to wait for this, so yield anyway.
+  // Note that the switchTab promise doesn't actually guarantee anything about *which*
+  // tab ends up as selected when its event fires, so using that here wouldn't work.
+  yield openedTabSelectedPromise;
   // should be switched back
   ok(openedTab.selected, "Ta-dah, the other tab should now be selected again!");
 

testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm

@@ -603,6 +603,34 @@ this.BrowserTestUtils = {
     return extra;
   }),
 
+  /**
+   * Returns a promise that is resolved when element gains attribute (or,
+   * optionally, when it is set to value).
+   * @param {String} attr
+   *        The attribute to wait for
+   * @param {Element} element
+   *        The element which should gain the attribute
+   * @param {String} value (optional)
+   *        Optional, the value the attribute should have.
+   *
+   * @returns {Promise}
+   */
+  waitForAttribute(attr, element, value) {
+    let MutationObserver = element.ownerDocument.defaultView.MutationObserver;
+    return new Promise(resolve => {
+      let mut = new MutationObserver(mutations => {
+        if ((!value && element.getAttribute(attr)) ||
+            (value && element.getAttribute(attr) === value)) {
+          resolve();
+          mut.disconnect();
+          return;
+        }
+      });
+
+      mut.observe(element, {attributeFilter: [attr]});
+    });
+  },
+
   /**
    * Version of EventUtils' `sendChar` function; it will synthesize a keypress
    * event in a child process and returns a Promise that will result when the