Document API methods.

GoogleSignIn/Sources/GIDKeychainHandler/Implementations/Fakes/GIDFakeKeychainHandler.h

@@ -22,6 +22,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface GIDFakeKeychainHandler : NSObject<GIDKeychainHandler>
 
+/// If YES, the method `saveAuthState:` returns NO and cleans the saved authState in the keychain.
+/// The default value is NO.
 @property(nonatomic) BOOL failToSave;
 
 @end

GoogleSignIn/Sources/GIDSignIn_Private.h

@@ -44,7 +44,9 @@ typedef void (^GIDUserAuthCompletion)(GIDUserAuth *_Nullable userAuth, NSError *
 /// Private initializer for |GIDSignIn|.
 - (instancetype)initPrivate;
 
-- (instancetype)initWithKeychainHandler:(id<GIDKeychainHandler>)keychainHandler;
+/// The designated initializer.
+- (instancetype)initWithKeychainHandler:(id<GIDKeychainHandler>)keychainHandler
+    NS_DESIGNATED_INITIALIZER;
 
 /// Authenticates with extra options.
 - (void)signInWithOptions:(GIDSignInInternalOptions *)options;