CREDENTIAL: Add 'PasswordCredential::toFormData()'

LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html

Index: LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html
diff --git a/LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html b/LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html
index f96de0b362abb155f45766a1874ba95ef3e7f9ec..96c784c7c200d213e10077245df05ab7beefe087 100644
--- a/LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html
+++ b/LayoutTests/http/tests/credentialmanager/credentialscontainer-get-basics.html
@@ -86,14 +86,14 @@ function stubRejectionChecker(reason) {
         verify_interface('PasswordCredential', c, {
             id: 'string',
             name: 'string',
-            iconURL: 'string',
-            password: 'string'
+            iconURL: 'string'
         });
 
         assert_equals(c.id, id);
         assert_equals(c.name, name);
         assert_equals(c.iconURL, icon);
-        assert_equals(c.password, password);
+        assert_true(c.toFormData() instanceof FormData);
+
         this.done();
     }