Convert Runtime.GetHandleForINativeObject to use GCHandle.

runtime/delegates.t4

@@ -121,7 +121,7 @@
 		},
 
 		new XDelegate ("id", "IntPtr", "xamarin_get_handle_for_inativeobject",
-			"MonoObject *", "IntPtr", "obj"
+			"GCHandle->MonoObject *", "IntPtr", "obj_handle"
 		) {
 			WrappedManagedFunction = "GetHandleForINativeObject",
 			OnlyDynamicUsage = false,

src/ObjCRuntime/Runtime.cs

@@ -649,7 +649,7 @@ namespace ObjCRuntime {
 
 		static IntPtr GetHandleForINativeObject (IntPtr ptr)
 		{
-			return ((INativeObject) ObjectWrapper.Convert (ptr)).Handle;
+			return ((INativeObject) GetGCHandleTarget (ptr)).Handle;
 		}
 
 		static void UnregisterNSObject (IntPtr native_obj, IntPtr managed_obj)