Make sure observers are not nullptr

base/observer_list.h

 // Copyright (c) 2011 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 BASE_OBSERVER_LIST_H__
 #define BASE_OBSERVER_LIST_H__
 
 #include <algorithm>
 #include <limits>
 #include <vector>
@@ skipping 136 matching lines @@
   ListType& observers = list_->observers_;
   // Advance if the current element is null
   size_t max_index = std::min(max_index_, observers.size());
   while (index_ < max_index && !observers[index_])
     ++index_;
   return index_ < max_index ? observers[index_++] : NULL;
 }
 
 template <class ObserverType>
 void ObserverListBase<ObserverType>::AddObserver(ObserverType* obs) {
+  DCHECK(obs);
   if (std::find(observers_.begin(), observers_.end(), obs)
       != observers_.end()) {
     NOTREACHED() << "Observers can only be added once!";
     return;
   }
   observers_.push_back(obs);
 }
 
 template <class ObserverType>
 void ObserverListBase<ObserverType>::RemoveObserver(ObserverType* obs) {
+  DCHECK(obs);
   typename ListType::iterator it =
     std::find(observers_.begin(), observers_.end(), obs);
   if (it != observers_.end()) {
     if (notify_depth_) {
       *it = 0;
     } else {
       observers_.erase(it);
     }
   }
 }
@@ skipping 55 matching lines @@
     if ((observer_list).might_have_observers()) {                        \
       ObserverListBase<ObserverType>::Iterator it_inside_observer_macro( \
           &observer_list);                                               \
       ObserverType* obs;                                                 \
       while ((obs = it_inside_observer_macro.GetNext()) != NULL)         \
         obs->func;                                                       \
     }                                                                    \
   } while (0)
 
 #endif  // BASE_OBSERVER_LIST_H__