CRBProtocolObservers can now be mutated while forwarding methods.

base/ios/crb_protocol_observers.h

 // Copyright 2014 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_IOS_CRB_PROTOCOL_OBSERVERS_H_
 #define BASE_IOS_CRB_PROTOCOL_OBSERVERS_H_
 
 #import <Foundation/Foundation.h>
 
 typedef void (^ExecutionWithObserverBlock)(id);
 
 // Implements a container for observers that implement a specific Objective-C
 // protocol. The container forwards method invocations to its contained
 // observers, so that sending a message to all the observers is as simple as
 // sending the message to the container.
+// It is safe for an observer to remove itself or another observer while being
+// notified. It is also safe to add an other observer while being notified but
+// the newly added observer will not be notified as part of the current
+// notification dispatch.
 @interface CRBProtocolObservers : NSObject
 
 // The Objective-C protocol that the observers in this container conform to.
 @property(nonatomic, readonly) Protocol* protocol;
 
 // Returns a CRBProtocolObservers container for observers that conform to
 // |protocol|.
-+ (CRBProtocolObservers*)observersWithProtocol:(Protocol*)protocol;
++ (instancetype)observersWithProtocol:(Protocol*)protocol;
 
 // Adds |observer| to this container.
 - (void)addObserver:(id)observer;
 
 // Remove |observer| from this container.
 - (void)removeObserver:(id)observer;
 
+// Returns true if there is currently no observers.

[stuartmorgan, 2015/06/04 13:40:05]

s/is/are/

[jbbegue, 2015/06/04 16:03:10]

Done.

+- (BOOL)empty;
+
 // Executes callback on every observer. |callback| cannot be nil.
 - (void)executeOnObservers:(ExecutionWithObserverBlock)callback;
 
 @end
 
 #endif  // BASE_IOS_CRB_PROTOCOL_OBSERVERS_H_