Add link with facebook credential (#527)

diff --git a/packages/firebase_auth/CHANGELOG.md b/packages/firebase_auth/CHANGELOG.md
index 11dd6e7..9ee0799 100644
--- a/packages/firebase_auth/CHANGELOG.md
+++ b/packages/firebase_auth/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.5.6
+
+* Added support for linkWithFacebookCredential
+
 ## 0.5.5
 
 * Updated Google Play Services dependencies to version 15.0.0.

diff --git a/packages/firebase_auth/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java b/packages/firebase_auth/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java
index fc4ca55..a42c591 100755
--- a/packages/firebase_auth/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java
+++ b/packages/firebase_auth/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java

@@ -89,6 +89,9 @@
       case "linkWithGoogleCredential":
         handleLinkWithGoogleCredential(call, result);
         break;
+      case "linkWithFacebookCredential":
+        handleLinkWithFacebookCredential(call, result);
+        break;
       case "updateProfile":
         handleUpdateProfile(call, result);
         break;
@@ -201,6 +204,17 @@
         .addOnCompleteListener(new SignInCompleteListener(result));
   }
 
+  private void handleLinkWithFacebookCredential(MethodCall call, final Result result) {
+    @SuppressWarnings("unchecked")
+    Map<String, String> arguments = (Map<String, String>) call.arguments;
+    String accessToken = arguments.get("accessToken");
+    AuthCredential credential = FacebookAuthProvider.getCredential(accessToken);
+    firebaseAuth
+        .getCurrentUser()
+        .linkWithCredential(credential)
+        .addOnCompleteListener(new SignInCompleteListener(result));
+  }
+
   private void handleSignInWithFacebook(MethodCall call, final Result result) {
     @SuppressWarnings("unchecked")
     Map<String, String> arguments = (Map<String, String>) call.arguments;

diff --git a/packages/firebase_auth/ios/Classes/FirebaseAuthPlugin.m b/packages/firebase_auth/ios/Classes/FirebaseAuthPlugin.m
index fb45411..86df706 100644
--- a/packages/firebase_auth/ios/Classes/FirebaseAuthPlugin.m
+++ b/packages/firebase_auth/ios/Classes/FirebaseAuthPlugin.m

@@ -146,6 +146,13 @@
                                         completion:^(FIRUser *user, NSError *error) {
                                           [self sendResult:result forUser:user error:error];
                                         }];
+  } else if ([@"linkWithFacebookCredential" isEqualToString:call.method]) {
+    NSString *accessToken = call.arguments[@"accessToken"];
+    FIRAuthCredential *credential = [FIRFacebookAuthProvider credentialWithAccessToken:accessToken];
+    [[FIRAuth auth].currentUser linkWithCredential:credential
+                                        completion:^(FIRUser *user, NSError *error) {
+                                          [self sendResult:result forUser:user error:error];
+                                        }];
   } else if ([@"updateProfile" isEqualToString:call.method]) {
     FIRUserProfileChangeRequest *changeRequest = [[FIRAuth auth].currentUser profileChangeRequest];
     if (call.arguments[@"displayName"]) {

diff --git a/packages/firebase_auth/lib/firebase_auth.dart b/packages/firebase_auth/lib/firebase_auth.dart
index 6a887de..1f814bb 100755
--- a/packages/firebase_auth/lib/firebase_auth.dart
+++ b/packages/firebase_auth/lib/firebase_auth.dart

@@ -309,6 +309,20 @@
     return currentUser;
   }
 
+  Future<FirebaseUser> linkWithFacebookCredential({
+    @required String accessToken,
+  }) async {
+    assert(accessToken != null);
+    final Map<dynamic, dynamic> data = await channel.invokeMethod(
+      'linkWithFacebookCredential',
+      <String, String>{
+        'accessToken': accessToken,
+      },
+    );
+    final FirebaseUser currentUser = new FirebaseUser._(data);
+    return currentUser;
+  }
+
   Future<Null> _callHandler(MethodCall call) async {
     switch (call.method) {
       case "onAuthStateChanged":

diff --git a/packages/firebase_auth/pubspec.yaml b/packages/firebase_auth/pubspec.yaml
index 2fc862d..27fca49 100755
--- a/packages/firebase_auth/pubspec.yaml
+++ b/packages/firebase_auth/pubspec.yaml

@@ -4,7 +4,7 @@
   and Twitter.
 author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/firebase_auth
-version: 0.5.5
+version: 0.5.6
 
 flutter:
   plugin: