Update from https://crrev.com/304121

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 82 matching lines @@
   explicit ObserverListBase(NotificationType type)
       : notify_depth_(0), type_(type) {}
 
   // Add an observer to the list.  An observer should not be added to
   // the same list more than once.
   void AddObserver(ObserverType* obs);
 
   // Remove an observer from the list if it is in the list.
   void RemoveObserver(ObserverType* obs);
 
-  bool HasObserver(ObserverType* observer) const;
+  // Determine whether a particular observer is in the list.
+  bool HasObserver(const ObserverType* observer) const;
 
   void Clear();
 
  protected:
   size_t size() const { return observers_.size(); }
 
   void Compact();
 
  private:
   friend class ObserverListThreadSafe<ObserverType>;
@@ skipping 55 matching lines @@
   if (it != observers_.end()) {
     if (notify_depth_) {
       *it = 0;
     } else {
       observers_.erase(it);
     }
   }
 }
 
 template <class ObserverType>
-bool ObserverListBase<ObserverType>::HasObserver(ObserverType* observer) const {
+bool ObserverListBase<ObserverType>::HasObserver(
+    const ObserverType* observer) const {
   for (size_t i = 0; i < observers_.size(); ++i) {
     if (observers_[i] == observer)
       return true;
   }
   return false;
 }
 
 template <class ObserverType>
 void ObserverListBase<ObserverType>::Clear() {
   if (notify_depth_) {
@@ skipping 41 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__