Work around a macOS 10.12 bug involving objects with weak delegates

chrome/browser/local_discovery/service_discovery_client_mac.mm

 // 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.
 
 #include "chrome/browser/local_discovery/service_discovery_client_mac.h"
 
 #import <arpa/inet.h>
 #import <Foundation/Foundation.h>
 #import <net/if_dl.h>
 #include <stddef.h>
@@ skipping 168 matching lines @@
     : service_type_(service_type),
       callback_(callback),
       callback_runner_(base::ThreadTaskRunnerHandle::Get()),
       service_discovery_runner_(service_discovery_runner),
       weak_factory_(this) {
 }
 
 ServiceWatcherImplMac::NetServiceBrowserContainer::
     ~NetServiceBrowserContainer() {
   DCHECK(IsOnServiceDiscoveryThread());
+
+  // Work around a 10.12 bug: NSNetServiceBrowser doesn't lose interest in its
+  // weak delegate during deallocation, so a subsequently-deallocated delegate
+  // attempts to clear the pointer to itself in an NSNetServiceBrowser that's
+  // already gone.
+  // https://crbug.com/657495, https://openradar.appspot.com/28943305
+  [browser_ setDelegate:nil];
 }
 
 void ServiceWatcherImplMac::NetServiceBrowserContainer::Start() {
   service_discovery_runner_->PostTask(
       FROM_HERE,
       base::Bind(&NetServiceBrowserContainer::StartOnDiscoveryThread,
                  weak_factory_.GetWeakPtr()));
 }
 
 void ServiceWatcherImplMac::NetServiceBrowserContainer::DiscoverNewServices() {
@@ skipping 93 matching lines @@
     scoped_refptr<base::SingleThreadTaskRunner> service_discovery_runner)
     : service_name_(service_name),
       callback_(callback),
       callback_runner_(base::ThreadTaskRunnerHandle::Get()),
       service_discovery_runner_(service_discovery_runner),
       weak_factory_(this) {
 }
 
 ServiceResolverImplMac::NetServiceContainer::~NetServiceContainer() {
   DCHECK(IsOnServiceDiscoveryThread());
+
+  // Work around a 10.12 bug: NSNetService doesn't lose interest in its weak
+  // delegate during deallocation, so a subsequently-deallocated delegate
+  // attempts to clear the pointer to itself in an NSNetService that's already
+  // gone.
+  // https://crbug.com/657495, https://openradar.appspot.com/28943305
+  [service_ setDelegate:nil];
 }
 
 void ServiceResolverImplMac::NetServiceContainer::StartResolving() {
   service_discovery_runner_->PostTask(
       FROM_HERE,
       base::Bind(&NetServiceContainer::StartResolvingOnDiscoveryThread,
                  weak_factory_.GetWeakPtr()));
 }
 
 void ServiceResolverImplMac::NetServiceContainer::DeleteSoon() {
@@ skipping 175 matching lines @@
   container_->OnResolveUpdate(local_discovery::ServiceResolver::STATUS_SUCCESS);
 }
 
 - (void)netService:(NSNetService*)sender
         didNotResolve:(NSDictionary*)errorDict {
   container_->OnResolveUpdate(
       local_discovery::ServiceResolver::STATUS_REQUEST_TIMEOUT);
 }
 
 @end