Fix retain cycles in RTCUIApplicationStatusObserver.

webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m

Index: webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
diff --git a/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m b/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
index 168832d9ed08a2653f2595f4f425203bde3d5f7a..64b1c73e10ac75ca81a5871bda6be905181d2a8e 100644
--- a/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
+++ b/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
@@ -16,12 +16,23 @@
 
 #include "webrtc/rtc_base/checks.h"
 
+@interface RTCUIApplicationStatusObserver ()
+
+@property(nonatomic, assign) UIApplicationState state;
+
+@end
+
 @implementation RTCUIApplicationStatusObserver {
   BOOL _initialized;
   dispatch_block_t _initializeBlock;
   UIApplicationState _state;
+
+  id<NSObject> _activeObserver;
+  id<NSObject> _backgroundObserver;
 }
 
+@synthesize state;
+
 + (instancetype)sharedInstance {
   static id sharedInstance;
   static dispatch_once_t onceToken;
@@ -35,19 +46,22 @@
 - (id)init {
   if (self = [super init]) {
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
-    [center addObserverForName:UIApplicationDidBecomeActiveNotification
-                        object:nil
-                         queue:[NSOperationQueue mainQueue]
-                    usingBlock:^(NSNotification *note) {
-                      _state = [UIApplication sharedApplication].applicationState;
-                    }];
-
-    [center addObserverForName:UIApplicationDidEnterBackgroundNotification
-                        object:nil
-                         queue:[NSOperationQueue mainQueue]
-                    usingBlock:^(NSNotification *note) {
-                      _state = [UIApplication sharedApplication].applicationState;
-                    }];
+    __weak RTCUIApplicationStatusObserver *weakSelf = self;
+    _activeObserver = [center addObserverForName:UIApplicationDidBecomeActiveNotification
+                                          object:nil
+                                           queue:[NSOperationQueue mainQueue]
+                                      usingBlock:^(NSNotification *note) {
+                                        weakSelf.state =
+                                            [UIApplication sharedApplication].applicationState;
+                                      }];
+
+    _backgroundObserver = [center addObserverForName:UIApplicationDidEnterBackgroundNotification
+                                              object:nil
+                                               queue:[NSOperationQueue mainQueue]
+                                          usingBlock:^(NSNotification *note) {
+                                            weakSelf.state =
+                                                [UIApplication sharedApplication].applicationState;
+                                          }];
 
     _initialized = NO;
     _initializeBlock = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS, ^{
@@ -61,6 +75,12 @@
   return self;
 }
 
+- (void)dealloc {
+  NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
+  [center removeObserver:_activeObserver];
+  [center removeObserver:_backgroundObserver];
+}
+
 - (BOOL)isApplicationActive {
   if (!_initialized) {
     long ret = dispatch_block_wait(_initializeBlock,