Add WaitForCondition() and use it in ExtensionTestNotificationObserver.

base/callback_list.h

 // This file was GENERATED by command:
 //     pump.py callback_list.h.pump
 // DO NOT EDIT BY HAND!!!
 
 
 // Copyright 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 BASE_CALLBACK_LIST_H_
@@ skipping 87 matching lines @@
    private:
     CallbackListBase<CallbackType>* list_;
     typename std::list<CallbackType>::iterator iter_;
 
     DISALLOW_COPY_AND_ASSIGN(Subscription);
   };
 
   // Add a callback to the list. The callback will remain registered until the
   // returned Subscription is destroyed, which must occur before the
   // CallbackList is destroyed.
-  scoped_ptr<Subscription> Add(const CallbackType& cb) {
+  scoped_ptr<Subscription> Add(const CallbackType& cb) WARN_UNUSED_RESULT {
     DCHECK(!cb.is_null());
     return scoped_ptr<Subscription>(
         new Subscription(this, callbacks_.insert(callbacks_.end(), cb)));
   }
 
  protected:
   // An iterator class that can be used to access the list of callbacks.
   class Iterator {
    public:
     explicit Iterator(CallbackListBase<CallbackType>* list)
@@ skipping 256 matching lines @@
     }
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CallbackList);
 };
 
 }  // namespace base
 
 #endif  // BASE_CALLBACK_LIST_H_