Fix bug in ObserverListThreadsafe::RemoveObserver

base/observer_list.h

 // Copyright (c) 2010 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__
 #pragma once
 
 #include <algorithm>
 #include <limits>
@@ skipping 93 matching lines @@
    private:
     ObserverListBase<ObserverType>& list_;
     size_t index_;
     size_t max_index_;
   };
 
   ObserverListBase() : notify_depth_(0), type_(NOTIFY_ALL) {}
   explicit ObserverListBase(NotificationType type)
       : notify_depth_(0), type_(type) {}
 
-  // Add an observer to the list.
+  // Add an observer to the list.  An observer should not be added to
+  // the same list more than once.
   void AddObserver(ObserverType* obs) {
-    DCHECK(find(observers_.begin(), observers_.end(), obs) == observers_.end())
-        << "Observers can only be added once!";
+    if (std::find(observers_.begin(), observers_.end(), obs)
+        != observers_.end()) {
+      NOTREACHED() << "Observers can only be added once!";
+      return;
+    }
     observers_.push_back(obs);
   }
 
-  // Remove an observer from the list.
+  // Remove an observer from the list if it is in the list.
   void RemoveObserver(ObserverType* 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 67 matching lines @@
 
 #define FOR_EACH_OBSERVER(ObserverType, observer_list, func)  \
   do {                                                        \
     ObserverListBase<ObserverType>::Iterator it(observer_list);   \
     ObserverType* obs;                                        \
     while ((obs = it.GetNext()) != NULL)                      \
       obs->func;                                              \
   } while (0)
 
 #endif  // BASE_OBSERVER_LIST_H__