Restore type attributes and remove extraneous nullability annotations for Objective-C Mac build

webrtc/api/objc/RTCMediaConstraints.mm

Index: webrtc/api/objc/RTCMediaConstraints.mm
diff --git a/webrtc/api/objc/RTCMediaConstraints.mm b/webrtc/api/objc/RTCMediaConstraints.mm
index 9d4e391d101b4af39c8edbd8a77df0d87c5e1005..bf50668e1d2120affdef2305950c8c891649c31c 100644
--- a/webrtc/api/objc/RTCMediaConstraints.mm
+++ b/webrtc/api/objc/RTCMediaConstraints.mm
@@ -13,8 +13,6 @@
 #import "webrtc/api/objc/RTCMediaConstraints+Private.h"
 #import "webrtc/base/objc/NSString+StdString.h"
 
-// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
-
 namespace webrtc {
 
 MediaConstraints::~MediaConstraints() {}
@@ -40,18 +38,14 @@ MediaConstraints::GetOptional() const {
 
 
 @implementation RTCMediaConstraints {
-  NSDictionary *_mandatory;
-  // NSDictionary<NSString *, NSString *> *_mandatory;
-  NSDictionary *_optional;
-  // NSDictionary<NSString *, NSString *> *_optional;
+  NSDictionary<NSString *, NSString *> *_mandatory;
+  NSDictionary<NSString *, NSString *> *_optional;
 }
 
 - (instancetype)initWithMandatoryConstraints:
-    (NSDictionary *)mandatory
-    // (NSDictionary<NSString *, NSString *> *)mandatory
+    (NSDictionary<NSString *, NSString *> *)mandatory
                          optionalConstraints:
-    (NSDictionary *)optional {
-    // (NSDictionary<NSString *, NSString *> *)optional {
+    (NSDictionary<NSString *, NSString *> *)optional {
   if (self = [super init]) {
     _mandatory = [[NSDictionary alloc] initWithDictionary:mandatory
                                                 copyItems:YES];
@@ -82,8 +76,7 @@ MediaConstraints::GetOptional() const {
 
 + (webrtc::MediaConstraintsInterface::Constraints)
     nativeConstraintsForConstraints:
-        (NSDictionary *)constraints {
-        // (NSDictionary<NSString *, NSString *> *)constraints {
+        (NSDictionary<NSString *, NSString *> *)constraints {
   webrtc::MediaConstraintsInterface::Constraints nativeConstraints;
   for (NSString *key in constraints) {
     NSAssert([key isKindOfClass:[NSString class]],