Bug 1415796 - Fix test failures of SessionStore if comformant Promise handling is applied. r=JanH

1. Improve BrowserApp._handleTabClosed() to remove Tab correctly if a new tab is
   added during "TabClose" dispatching.
2. Resolve "load" event in next event tick to simulate visiting a different page
   properly, so the session history will be added correctly.

mobile/android/chrome/content/browser.js

@@ -1279,6 +1279,9 @@ var BrowserApp = {
       }
     }
 
+    // Retrieve updated tabIndex again for the removal because the index could
+    // be changed if a new tab is added by the event listener.
+    tabIndex = this._tabs.indexOf(aTab);
     aTab.destroy();
     this._tabs.splice(tabIndex, 1);
   },

mobile/android/tests/browser/chrome/head.js

@@ -5,7 +5,7 @@ function fuzzyEquals(a, b) {
   return (Math.abs(a - b) < 1e-6);
 }
 
-function promiseBrowserEvent(browser, eventType) {
+function promiseBrowserEvent(browser, eventType, options) {
   return new Promise((resolve) => {
     function handle(event) {
       // Since we'll be redirecting, don't make assumptions about the given URL and the loaded URL
@@ -15,7 +15,11 @@ function promiseBrowserEvent(browser, eventType) {
       }
       info("Received event " + eventType + " from browser");
       browser.removeEventListener(eventType, handle, true);
-      resolve(event);
+      if (options && options.resolveAtNextTick) {
+        setTimeout(() => resolve(event), 0);
+      } else {
+        resolve(event);
+      }
     }
 
     browser.addEventListener(eventType, handle, true);

mobile/android/tests/browser/chrome/test_session_form_data.html

@@ -96,7 +96,7 @@ add_task(function* test_formdata() {
       // Create a new tab.
       let tab = gBrowserApp.addTab(URL);
       let browser = tab.browser;
-      yield promiseBrowserEvent(browser, "load");
+      yield promiseBrowserEvent(browser, "load", { resolveAtNextTick: true });
 
       // Modify form data.
       setInputValue(browser, {id: "txt", value: OUTER_VALUE});
@@ -151,7 +151,7 @@ add_task(function* test_formdata2() {
       // Create a new tab.
       let tab = gBrowserApp.addTab(URL);
       let browser = tab.browser;
-      yield promiseBrowserEvent(browser, "load");
+      yield promiseBrowserEvent(browser, "load", { resolveAtNextTick: true });
 
       // Modify form data.
       setInputValue(browser, {id: "txt", value: OUTER_VALUE});
@@ -172,7 +172,7 @@ add_task(function* test_formdata2() {
   // Restore the closed tab.
   let closedTabData = ss.getClosedTabs(gChromeWin)[0];
   let browser = ss.undoCloseTab(gChromeWin, closedTabData);
-  yield promiseBrowserEvent(browser, "load");
+  yield promiseBrowserEvent(browser, "load", { resolveAtNextTick: true });
 
   // Check the form data.
   is(getInputValue(browser, {id: "txt"}), OUTER_VALUE, "outer value restored correctly");
@@ -211,7 +211,7 @@ add_task(function* test_formdata_navigation() {
       // Create a new tab.
       let tab = gBrowserApp.addTab(URL);
       let browser = tab.browser;
-      yield promiseBrowserEvent(browser, "load");
+      yield promiseBrowserEvent(browser, "load", { resolveAtNextTick: true });
 
       // Modify form data.
       setInputValue(browser, {id: "txt", value: OUTER_VALUE});
@@ -251,7 +251,7 @@ add_task(function* test_formdata_navigation() {
   // Restore the closed tab.
   let closedTabData = ss.getClosedTabs(gChromeWin)[0];
   let browser = ss.undoCloseTab(gChromeWin, closedTabData);
-  yield promiseBrowserEvent(browser, "load");
+  yield promiseBrowserEvent(browser, "load", { resolveAtNextTick: true });
 
   // Check the form data.
   is(getInputValue(browser, {id: "txt"}), OUTER_VALUE, "outer value restored correctly");