ObserverList::HasObserver now takes a const pointer.

chromeos/dbus/system_clock_client.h

 // Copyright (c) 2013 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 CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_
 #define CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_
 
 #include "base/callback.h"
 #include "chromeos/chromeos_export.h"
 #include "chromeos/dbus/dbus_client.h"
@@ skipping 17 matching lines @@
     virtual ~Observer() {}
   };
 
   virtual ~SystemClockClient();
 
   // Adds the given observer.
   virtual void AddObserver(Observer* observer) = 0;
   // Removes the given observer if this object has the observer.
   virtual void RemoveObserver(Observer* observer) = 0;
   // Returns true if this object has the given observer.
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // Sets the system clock.
   virtual void SetTime(int64 time_in_seconds) = 0;
 
   // Checks if the system time can be set.
   virtual bool CanSetTime() = 0;
 
   // Creates the instance.
   static SystemClockClient* Create();
 
  protected:
   // Create() should be used instead.
   SystemClockClient();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SystemClockClient);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_