Credential Management: Add 'Credential::type' attribute.

Source/platform/exported/WebCredential.cpp

Index: Source/platform/exported/WebCredential.cpp
diff --git a/Source/platform/exported/WebCredential.cpp b/Source/platform/exported/WebCredential.cpp
index e08d1aecd373d83b18421799fa47f32ae19f0ec7..d4e678e30dd24fc7bdaf851e825e03c18b2cfb90 100644
--- a/Source/platform/exported/WebCredential.cpp
+++ b/Source/platform/exported/WebCredential.cpp
@@ -73,6 +73,11 @@ WebURL WebCredential::avatarURL() const
     return m_platformCredential->avatarURL();
 }
 
+WebString WebCredential::type() const
+{
+    return m_platformCredential->type();
+}
+
 bool WebCredential::isLocalCredential() const
 {
     return m_platformCredential->isLocal();