CREDENTIAL: Teach Fetch to handle PasswordCredential objects.

third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl

Index: third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl
diff --git a/third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl b/third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl
index 8c4d81bb83eaf362d4f74d77ef6cdd58233f5293..b85b862fdebc0efbb9b3f98fe7df88d481643ecd 100644
--- a/third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl
+++ b/third_party/WebKit/Source/modules/credentialmanager/PasswordCredential.idl
@@ -2,11 +2,19 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// TODO(mkwst): I think the '?' should be down with the nullable attribute
+// rather than up here with the `typedef`, but that generates bindings code
+// that doesn't compile. https://crbug.com/557742
+typedef (FormData or URLSearchParams)? CredentialBodyType;
+
 [
     RuntimeEnabled=CredentialManager,
     RaisesException=Constructor,
     Constructor(PasswordCredentialData data),
-    Exposed=Window
+    Exposed=Window,
+    TypeChecking=Interface
 ] interface PasswordCredential : Credential {
-    [CallWith=ScriptState] FormData toFormData(optional FormDataOptions options);
+    attribute USVString idName;
+    attribute USVString passwordName;
+    attribute CredentialBodyType additionalData;
 };