Fix crash when accessing automation node from stale AX tree

chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js

Index: chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js
diff --git a/chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js b/chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js
index bb2d619b8c05af6f8118e08ed3851d905a2d596a..aa04332d65849bcbf2d4987c0051b79023505278 100644
--- a/chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js
+++ b/chrome/test/data/extensions/api_test/automation/tests/tabs/close_tab.js
@@ -8,10 +8,15 @@ var allTests = [
       chrome.tabs.create({'url': url}, function(tab) {
         chrome.automation.getTree(function(rootNode) {
           rootNode.addEventListener(EventType.destroyed, function() {
-            // Should get a 'destroyed' event when the tab is closed.
-            // TODO(aboxhall): assert actual cleanup has occurred once
-            // crbug.com/387954 makes it possible.
-            chrome.test.succeed();
+            // Poll until the root node doesn't have a role anymore

[David Tseng, 2015/08/28 22:51:25]

Do we get an event (as to avoid busy waiting?).

[dmazzoni, 2015/08/28 23:02:35]

We get the event immediately before it's destroyed - this is on purpose, so you
can figure out *what* got destroyed. So a setTimeout(0) would work in that
immediately afterwards, that node will be invalid.

I didn't want to depend on setTimeout(0), though, I thought it'd be more robust
to basically say the test busy-waits until the node becomes invalid (which it
should do quickly).

+            // indicating that it really did get cleaned up.
+            function checkSuccess() {
+              if (rootNode.role === undefined)
+                chrome.test.succeed();
+              else
+                window.setTimeout(checkSuccess, 10);
+            }
+            checkSuccess();
           });
           chrome.tabs.remove(tab.id);
         });