Tolerate GetRoot() returning null.

content/browser/accessibility/browser_accessibility_manager_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/accessibility/browser_accessibility_manager_win.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/win/scoped_comptr.h"
@@ skipping 132 matching lines @@
 
   // Set this flag so that we'll keep trying to fire these focus events
   // if they're not successful this time.
   focus_event_on_root_needed_ = true;
 
   if (!delegate_ || !delegate_->AccessibilityViewHasFocus())
     return;
 
   // Try to fire a focus event on the root first and then the focused node.
   // This will clear focus_event_on_root_needed_ if successful.
-  if (focus_ != tree_->root())
+  if (focus_ != tree_->root() && GetRoot())
     NotifyAccessibilityEvent(ui::AX_EVENT_FOCUS, GetRoot());
   BrowserAccessibilityManager::OnWindowFocused();
 }
 
 void BrowserAccessibilityManagerWin::UserIsReloading() {
-  MaybeCallNotifyWinEvent(IA2_EVENT_DOCUMENT_RELOAD, GetRoot());
+  if (GetRoot())
+    MaybeCallNotifyWinEvent(IA2_EVENT_DOCUMENT_RELOAD, GetRoot());
 }
 
 void BrowserAccessibilityManagerWin::NotifyAccessibilityEvent(
     ui::AXEvent event_type,
     BrowserAccessibility* node) {
   BrowserAccessibilityDelegate* root_delegate = GetDelegateFromRootManager();
   if (!root_delegate || !root_delegate->AccessibilityGetAcceleratedWidget()) {
     LOG(WARNING) << "Not firing AX event because of no root_delegate or hwnd";
     return;
   }
@@ skipping 76 matching lines @@
       break;
     case ui::AX_EVENT_TEXT_SELECTION_CHANGED:
       event_id = IA2_EVENT_TEXT_CARET_MOVED;
       break;
     default:
       // Not all WebKit accessibility events result in a Windows
       // accessibility notification.
       break;
   }
 
+  if (!node)
+    return;
+
   if (event_id != EVENT_MIN) {
     // Pass the node's unique id in the |child_id| argument to NotifyWinEvent;
     // the AT client will then call get_accChild on the HWND's accessibility
     // object and pass it that same id, which we can use to retrieve the
     // IAccessible for this node.
     MaybeCallNotifyWinEvent(event_id, node);
   }
 
   // If this is a layout complete notification (sent when a container scrolls)
   // and there is a descendant tracked object, send a notification on it.
@@ skipping 115 matching lines @@
           child_manager->GetFromUniqueIdWin(unique_id_win);
       if (result)
         return result;
     }
   }
 
   return NULL;
 }
 
 }  // namespace content