Bug 1167508 - Fix BrowserTestUtils.browserLoaded() and use it in sessionstore/head.js r=billm

browser/components/sessionstore/test/head.js

@@ -282,14 +282,7 @@ let promiseForEachSessionRestoreFile = Task.async(function*(cb) {
 });
 
 function promiseBrowserLoaded(aBrowser, ignoreSubFrames = true) {
-  return new Promise(resolve => {
-    aBrowser.messageManager.addMessageListener("ss-test:loadEvent", function onLoad(msg) {
-      if (!ignoreSubFrames || !msg.data.subframe) {
-        aBrowser.messageManager.removeMessageListener("ss-test:loadEvent", onLoad);
-        resolve();
-      }
-    });
-  });
+  return BrowserTestUtils.browserLoaded(aBrowser, !ignoreSubFrames);
 }
 
 function whenWindowLoaded(aWindow, aCallback = next) {

testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm

@@ -140,11 +140,10 @@ this.BrowserTestUtils = {
    */
   browserLoaded(browser, includeSubFrames=false) {
     return new Promise(resolve => {
-      browser.messageManager.addMessageListener("browser-test-utils:loadEvent",
-                                                 function onLoad(msg) {
-        if (!msg.data.subframe || includeSubFrames) {
-          browser.messageManager.removeMessageListener(
-            "browser-test-utils:loadEvent", onLoad);
+      let mm = browser.ownerDocument.defaultView.messageManager;
+      mm.addMessageListener("browser-test-utils:loadEvent", function onLoad(msg) {
+        if (msg.target == browser && (!msg.data.subframe || includeSubFrames)) {
+          mm.removeMessageListener("browser-test-utils:loadEvent", onLoad);
           resolve();
         }
       });