Fixes to get view_manager_lib_unittests not crash

mojo/examples/window_manager/window_manager.cc

 // Copyright 2014 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 "base/basictypes.h"
 #include "base/bind.h"
 #include "mojo/examples/keyboard/keyboard.mojom.h"
 #include "mojo/examples/window_manager/debug_panel.h"
 #include "mojo/examples/window_manager/window_manager.mojom.h"
 #include "mojo/public/c/system/main.h"
@@ skipping 247 matching lines @@
  public:
   WindowManager()
       : window_manager_factory_(this),
         navigator_host_factory_(this),
         launcher_ui_(NULL),
         view_manager_(NULL),
         window_manager_app_(new WindowManagerApp(this, this)),
         app_(NULL) {}
 
   virtual ~WindowManager() {
-    window_manager_app_->host()->window()->RemovePreTargetHandler(this);
+    // host() may be destroyed by the time we get here.
+    // TODO: figure out a way to always cleanly remove handler.
+    if (window_manager_app_->host())
+      window_manager_app_->host()->window()->RemovePreTargetHandler(this);
   }
 
   void CloseWindow(Id view_id) {
     View* view = view_manager_->GetViewById(view_id);
     DCHECK(view);
     std::vector<View*>::iterator iter =
         std::find(windows_.begin(), windows_.end(), view);
     DCHECK(iter != windows_.end());
     windows_.erase(iter);
     view->Destroy();
@@ skipping 282 matching lines @@
   window_manager_->RequestNavigate(source_view_id, target, nav_details.Pass());
 }
 
 }  // namespace examples
 }  // namespace mojo
 
 MojoResult MojoMain(MojoHandle shell_handle) {
   mojo::ApplicationRunnerChromium runner(new mojo::examples::WindowManager);
   return runner.Run(shell_handle);
 }