Add WaitForCondition() and use it in ExtensionTestNotificationObserver.

base/callback_list.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
 $$
 $$ http://code.google.com/p/googletest/wiki/PumpManual
 $$
 
 $$ See comment for MAX_ARITY in base/bind.h.pump.
 $var MAX_ARITY = 7
 
@@ skipping 92 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 114 matching lines @@
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CallbackList);
 };
 
 
 ]]  $$ for ARITY
 }  // namespace base
 
 #endif  // BASE_CALLBACK_LIST_H_