Fix ArcAccessibilityHelperBridgeTest.NotificationEventArriveFirst

Bug: 817264
Test: ArcAccessibilityHelperBridgeTest.NotificationEventArriveFirst
Change-Id: Id9c90466a335680355ac83fc6d8b70a387c53b99
Reviewed-on: https://chromium-review.googlesource.com/940902Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Yuki Awano <yawano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539755}

chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge_unittest.cc

@@ -318,7 +318,7 @@ TEST_F(ArcAccessibilityHelperBridgeTest, NotificationEventArriveFirst) {
   // expected behavior.
   auto it2 = notification_key_to_tree_.find(kNotificationKey);
   EXPECT_NE(notification_key_to_tree_.end(), it2);
-  AXTreeSourceArc* tree2 = it->second.get();
+  AXTreeSourceArc* tree2 = it2->second.get();
   ui::AXTreeData tree_data2;
   tree2->GetTreeData(&tree_data2);
   EXPECT_EQ(tree_data2.tree_id, test_surface.GetAXTreeId());