Change O(n^2) loop to O(n) in ObserverListBase::Compact().

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__
 #pragma once
 
 #include <algorithm>
 #include <limits>
@@ skipping 144 matching lines @@
       }
     } else {
       observers_.clear();
     }
   }
 
   size_t size() const { return observers_.size(); }
 
  protected:
   void Compact() {
-    typename ListType::iterator it = observers_.begin();
-    while (it != observers_.end()) {
-      if (*it) {
-        ++it;
-      } else {
-        it = observers_.erase(it);
-      }
-    }
+    observers_.erase(
+        std::remove(observers_.begin(), observers_.end(),
+                    static_cast<ObserverType*>(NULL)), observers_.end());
   }
 
  private:
   friend class ObserverListThreadSafe<ObserverType>;
 
   typedef std::vector<ObserverType*> ListType;
 
   ListType observers_;
   int notify_depth_;
   NotificationType type_;
@@ skipping 30 matching lines @@
   do {                                                               \
     if ((observer_list).might_have_observers()) {                    \
       ObserverListBase<ObserverType>::Iterator it(observer_list);    \
       ObserverType* obs;                                             \
       while ((obs = it.GetNext()) != NULL)                           \
         obs->func;                                                   \
     }                                                                \
   } while (0)
 
 #endif  // BASE_OBSERVER_LIST_H__