Credential Manager: Add platform-exposed Credential objects.

Source/modules/credentialmanager/Credential.cpp

Index: Source/modules/credentialmanager/Credential.cpp
diff --git a/Source/modules/credentialmanager/Credential.cpp b/Source/modules/credentialmanager/Credential.cpp
index 1be4918aa38aa864f1adb9b0ae2c75767b9e20d0..24b220054437fb8d877be79fb3f0947b9ed157f0 100644
--- a/Source/modules/credentialmanager/Credential.cpp
+++ b/Source/modules/credentialmanager/Credential.cpp
@@ -12,14 +12,22 @@ Credential* Credential::create(const String& id, const String& name, const Strin
     return new Credential(id, name, avatarURL);
 }
 
+Credential::Credential(PlatformCredential* credential)
+    : m_private(credential)
+{
+}
+
 Credential::Credential(const String& id, const String& name, const String& avatarURL)
-    : m_id(id)
-    , m_name(name)
-    , m_avatarURL(avatarURL)
+    : m_private(PlatformCredential::create(id, name, avatarURL))
 {
     ScriptWrappable::init(this);
 }
 
+void Credential::trace(Visitor* visitor)
+{
+    visitor->trace(m_private);
+}
+
 Credential::~Credential()
 {
 }