Adding Discarded property support for onUpdate function.

chrome/test/data/extensions/api_test/tabs/basics/discarded.js

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.

[Devlin, 2016/07/29 16:01:09]

ditto

[Anderson Silva, 2016/07/29 19:05:59]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var testTab;
+chrome.test.runTests([
+
+    function setupWindow() {
+      var testTabId;
+
+      createWindow(["about:blank", "chrome://newtab/"], {},
+        pass(function (winId, tabIds) {
+          testTabId = tabIds[1];
+      }));
+
+      waitForAllTabs(pass(function () {
+        queryForTab(testTabId, {}, pass(function (tab) {
+          testTab = tab;
+        }));
+      }));
+    },
+
+    function discard() {
+      // Initially tab isn't discarded.
+      assertFalse(testTab.discarded);
+
+      var onUpdatedCompleted = chrome.test.listenForever(
+        chrome.tabs.onUpdated,
+        function (tabId, changeInfo, tab) {
+          if ('discarded' in changeInfo) {
+            // Make sure it's the right tab.
+            assertEq(testTab.index, tab.index);
+            assertEq(testTab.windowId, tab.windowId);
+
+            // Make sure the discarded state changed correctly.
+            assertTrue(changeInfo.discarded);
+            assertTrue(tab.discarded);
+
+            onUpdatedCompleted();
+          }
+        }
+      );
+
+      // Discard and update testTab (the id changes after a tab is discarded).

[Devlin, 2016/07/29 16:01:09]

The id changes?  That's a bit yucky.  We normally guarantee the id to remain
constant for a tab's lifetime.  Is there a reason it needs to change?

[Anderson Silva, 2016/07/29 19:05:59]

Yeah, you're right, this is weird. But it isn't related to this, it's an issue
because when the tab is discarded the old web_contents is deleted and a new one
is created with a new assigned id. 
We'll look deeper on this issue to try to find if we can maintain the id.

[Devlin, 2016/07/29 20:17:33]

Cool, thanks!  I don't want to block this issue on that, but can you add a TODO
here (and maybe file a bug if there isn't one?) so that we can track this?

+      chrome.tabs.discard(testTab.id, pass(function (tab) {
+        assertTrue(tab.discarded);
+        testTab = tab;
+      }));
+    },
+
+  function reload() {
+    // Tab is already discarded.
+    assertTrue(testTab.discarded);
+
+    var onUpdatedCompleted = chrome.test.listenForever(
+      chrome.tabs.onUpdated,
+      function (tabId, changeInfo, tab) {
+        if ('discarded' in changeInfo) {
+          // Make sure it's the right tab.
+          assertEq(testTab.index, tab.index);
+          assertEq(testTab.windowId, tab.windowId);
+
+          // Make sure the discarded state changed correctly.
+          assertFalse(changeInfo.discarded);
+          assertFalse(tab.discarded);
+
+          onUpdatedCompleted();
+        }
+      }
+    );
+
+    chrome.tabs.reload(testTab.id);
+  }
+]);