Add support for initializing custom domains without Core. This is required for 1P. (#3540)

Example/DynamicLinks/Tests/FIRDynamicLinksTest.m

@@ -513,6 +513,27 @@ static NSString *const kInfoPlistCustomDomainsKey = @"FirebaseDynamicLinksCustom
   XCTAssertNil(dynamicLink, @"invite should be nil since there is no parameter.");
 }
 
+// Custom domain entries in plist file:
+//  https://google.com
+//  https://google.com/one
+//  https://a.firebase.com/mypath
+- (void)testDynamicLinkFromUniversalLinkURLWithCustomDomainLink {
+  self.service = [[FIRDynamicLinks alloc] init];
+  NSString *durableDeepLinkString = @"https://a.firebase.com/mypath/?link=abcd";
+  NSURL *durabledeepLinkURL = [NSURL URLWithString:durableDeepLinkString];
+
+  SwizzleDynamicLinkNetworkingWithMock();
+
+  FIRDynamicLink *dynamicLink = [self.service dynamicLinkFromUniversalLinkURL:durabledeepLinkURL];
+
+  XCTAssertNotNil(dynamicLink);
+  NSString *deepLinkURLString = dynamicLink.url.absoluteString;
+
+  XCTAssertEqualObjects(@"abcd", deepLinkURLString,
+                        @"ddl url parameter and deep link url should be the same");
+  UnswizzleDynamicLinkNetworking();
+}
+
 - (void)testDynamicLinkFromUniversalLinkURLWithSpecialCharacters {
   NSString *durableDeepLinkString =
       [NSString stringWithFormat:@"https://xyz.page.link/?link=%@", kEncodedComplicatedURLString];

Firebase/DynamicLinks/FIRDynamicLinks.m

@@ -220,12 +220,7 @@ static const NSInteger FIRErrorCodeDurableDeepLinkFailed = -119;
     }
     [NSException raise:kFirebaseDurableDeepLinkErrorDomain format:@"%@", message];
   }
-  // Check to see if FirebaseDynamicLinksCustomDomains array is present.
-  NSDictionary *infoDictionary = [NSBundle mainBundle].infoDictionary;
-  NSArray *customDomains = infoDictionary[kInfoPlistCustomDomainsKey];
-  if (customDomains) {
-    FIRDLAddToAllowListForCustomDomainsArray(customDomains);
-  }
+  [self checkForCustomDomainEntriesInInfoPlist];
 }
 
 - (instancetype)initWithAnalytics:(nullable id<FIRAnalyticsInterop>)analytics {
@@ -254,6 +249,26 @@ static const NSInteger FIRErrorCodeDurableDeepLinkFailed = -119;
 }
 #endif
 
+#pragma mark - Custom domains
+
+- (instancetype)init {
+  self = [super init];
+  if (self) {
+    [self checkForCustomDomainEntriesInInfoPlist];
+  }
+  return self;
+}
+
+// Check for custom domains entry in PLIST file.
+- (void)checkForCustomDomainEntriesInInfoPlist {
+  // Check to see if FirebaseDynamicLinksCustomDomains array is present.
+  NSDictionary *infoDictionary = [NSBundle mainBundle].infoDictionary;
+  NSArray *customDomains = infoDictionary[kInfoPlistCustomDomainsKey];
+  if (customDomains) {
+    FIRDLAddToAllowListForCustomDomainsArray(customDomains);
+  }
+}
+
 #pragma mark - First party interface
 
 - (BOOL)setUpWithLaunchOptions:(nullable NSDictionary *)launchOptions