Update from https://crrev.com/316786

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.
+@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;
+
+// Adds |observer| to this container.
+- (void)addObserver:(id)observer;
+
+// Remove |observer| from this container.
+- (void)removeObserver:(id)observer;
+
+// Executes callback on every observer. |callback| cannot be nil.
+- (void)executeOnObservers:(ExecutionWithObserverBlock)callback;
+
+@end
+
+#endif  // BASE_IOS_CRB_PROTOCOL_OBSERVERS_H_