Revert "content: convert accessibility notifications to callbacks"

content/browser/accessibility/cross_platform_accessibility_browsertest.cc

Index: content/browser/accessibility/cross_platform_accessibility_browsertest.cc
diff --git a/content/browser/accessibility/cross_platform_accessibility_browsertest.cc b/content/browser/accessibility/cross_platform_accessibility_browsertest.cc
index fd3c4bd468aec1ca89bdef43aee6b3307e83856a..7135283930cfb1e5c79fd191bd30d1d112e5dcea 100644
--- a/content/browser/accessibility/cross_platform_accessibility_browsertest.cc
+++ b/content/browser/accessibility/cross_platform_accessibility_browsertest.cc
@@ -33,17 +33,17 @@ class CrossPlatformAccessibilityBrowserTest : public ContentBrowserTest {
   // notification that it's been received.
   const AccessibilityNodeData& GetAccessibilityNodeDataTree(
       AccessibilityMode accessibility_mode = AccessibilityModeComplete) {
-    scoped_refptr<MessageLoopRunner> loop_runner(new MessageLoopRunner);
+    WindowedNotificationObserver tree_updated_observer(
+        NOTIFICATION_ACCESSIBILITY_LAYOUT_COMPLETE,
+        NotificationService::AllSources());
     RenderWidgetHostView* host_view =
         shell()->web_contents()->GetRenderWidgetHostView();
     RenderWidgetHostImpl* host =
         RenderWidgetHostImpl::From(host_view->GetRenderWidgetHost());
     RenderViewHostImpl* view_host = static_cast<RenderViewHostImpl*>(host);
-    view_host->SetAccessibilityLayoutCompleteCallbackForTesting(
-        loop_runner->QuitClosure());
     view_host->set_save_accessibility_tree_for_testing(true);
     view_host->SetAccessibilityMode(accessibility_mode);
-    loop_runner->Run();
+    tree_updated_observer.Wait();
     return view_host->accessibility_tree_for_testing();
   }