Oilpan: make DOMWindowProperty a GC mixin.

Source/modules/credentialmanager/NavigatorCredentials.cpp

Index: Source/modules/credentialmanager/NavigatorCredentials.cpp
diff --git a/Source/modules/credentialmanager/NavigatorCredentials.cpp b/Source/modules/credentialmanager/NavigatorCredentials.cpp
index 2cb6dc1f8c8946afc2275d8b1f886e1f5639bb1c..17679a67974dea4c30b3ffc839984fd5232ab302 100644
--- a/Source/modules/credentialmanager/NavigatorCredentials.cpp
+++ b/Source/modules/credentialmanager/NavigatorCredentials.cpp
@@ -18,9 +18,7 @@ NavigatorCredentials::NavigatorCredentials(Navigator& navigator)
 {
 }
 
-NavigatorCredentials::~NavigatorCredentials()
-{
-}
+DEFINE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(NavigatorCredentials);
 
 NavigatorCredentials& NavigatorCredentials::from(Navigator& navigator)
 {
@@ -53,6 +51,7 @@ void NavigatorCredentials::trace(Visitor* visitor)
 {
     visitor->trace(m_credentialsContainer);
     WillBeHeapSupplement<Navigator>::trace(visitor);
+    DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink