Fixed crash when PCF is destroyed before PC in ObjC

Bug: webrtc:9231
Change-Id: Iaf18257b8f38fa786d462bca5f860f9a7b1cc2d0
Reviewed-on: https://webrtc-review.googlesource.com/78800
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23674}

sdk/objc/Framework/Classes/PeerConnection/RTCPeerConnection.mm

@@ -240,6 +240,7 @@ void PeerConnectionDelegateAdapter::OnAddTrack(
 
 
 @implementation RTCPeerConnection {
+  RTCPeerConnectionFactory *_factory;
   NSMutableArray<RTCMediaStream *> *_localStreams;
   std::unique_ptr<webrtc::PeerConnectionDelegateAdapter> _observer;
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> _peerConnection;
@@ -272,6 +273,7 @@ void PeerConnectionDelegateAdapter::OnAddTrack(
     if (!_peerConnection) {
       return nil;
     }
+    _factory = factory;
     _localStreams = [[NSMutableArray alloc] init];
     _delegate = delegate;
   }

sdk/objc/Framework/UnitTests/RTCPeerConnectionFactory_xctest.m

@@ -0,0 +1,45 @@
+/*
+ *  Copyright 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#import <WebRTC/RTCConfiguration.h>
+#import <WebRTC/RTCMediaConstraints.h>
+#import <WebRTC/RTCPeerConnection.h>
+#import <WebRTC/RTCPeerConnectionFactory.h>
+
+#import <XCTest/XCTest.h>
+
+@interface RTCPeerConnectionFactoryTests : XCTestCase
+- (void)testPeerConnectionLifetime;
+@end
+
+@implementation RTCPeerConnectionFactoryTests
+
+- (void)testPeerConnectionLifetime {
+  @autoreleasepool {
+    RTCConfiguration *config = [[RTCConfiguration alloc] init];
+
+    RTCMediaConstraints *contraints =
+        [[RTCMediaConstraints alloc] initWithMandatoryConstraints:@{} optionalConstraints:nil];
+
+    RTCPeerConnectionFactory *factory = [[RTCPeerConnectionFactory alloc] init];
+
+    RTCPeerConnection *peerConnection =
+        [factory peerConnectionWithConfiguration:config constraints:contraints delegate:nil];
+
+    [peerConnection close];
+
+    factory = nil;
+    peerConnection = nil;
+  }
+
+  XCTAssertTrue(true, @"Expect test does not crash");
+}
+
+@end