Relanding focus manager refactoring

views/focus/external_focus_tracker.cc

 // Copyright (c) 2006-2008 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 "views/focus/external_focus_tracker.h"
 
+#include "base/logging.h"
 #include "views/view.h"
 #include "views/focus/view_storage.h"
 
 namespace views {
 
 ExternalFocusTracker::ExternalFocusTracker(View* parent_view,
                                            FocusManager* focus_manager)
     : focus_manager_(focus_manager),
       parent_view_(parent_view) {
+  DCHECK(focus_manager);
+  DCHECK(parent_view);
   view_storage_ = ViewStorage::GetSharedInstance();
   last_focused_view_storage_id_ = view_storage_->CreateStorageID();
   // Store the view which is focused when we're created.
   StartTracking();
 }
 
 ExternalFocusTracker::~ExternalFocusTracker() {
   view_storage_->RemoveView(last_focused_view_storage_id_);
   if (focus_manager_)
     focus_manager_->RemoveFocusChangeListener(this);
@@ skipping 30 matching lines @@
   if (view != NULL)
     view_storage_->StoreView(last_focused_view_storage_id_, view);
 }
 
 void ExternalFocusTracker::StartTracking() {
   StoreLastFocusedView(focus_manager_->GetFocusedView());
   focus_manager_->AddFocusChangeListener(this);
 }
 
 }  // namespace views