Fix a crasher with "select file" dialogs.

app/win/window_impl.h

 // Copyright (c) 2009 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.
 
 #ifndef APP_WIN_WINDOW_IMPL_H_
 #define APP_WIN_WINDOW_IMPL_H_
 
 #include <atlbase.h>
 #include <atlapp.h>
 #include <atlmisc.h>
@@ skipping 52 matching lines @@
   DWORD window_ex_style() const { return window_ex_style_; }
 
   // Sets the class style to use. The default is CS_DBLCLKS.
   void set_initial_class_style(UINT class_style) {
     // We dynamically generate the class name, so don't register it globally!
     DCHECK_EQ((class_style & CS_GLOBALCLASS), 0);
     class_style_ = class_style;
   }
   UINT initial_class_style() const { return class_style_; }
 
+  // Returns true if the specified |hwnd| is a WindowImpl.
+  static bool IsWindowImpl(HWND hwnd);
+
  protected:
   // Handles the WndProc callback for this object.
   virtual LRESULT OnWndProc(UINT message, WPARAM w_param, LPARAM l_param);
 
  private:
   friend class ClassRegistrar;
 
   // The window procedure used by all Windows.
   static LRESULT CALLBACK WndProc(HWND window,
                                   UINT message,
@@ skipping 18 matching lines @@
 
   // Our hwnd.
   HWND hwnd_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowImpl);
 };
 
 }  // namespace app
 
 #endif  // APP_WIN_WINDOW_IMPL_H_