Move WeakReference setup to separate method.

Trying to fix #655.

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Direct.cs

@@ -360,15 +360,7 @@ namespace Avalonia.Base.UnitTests
         public void Binding_To_Direct_Property_Gets_Collected_When_Completed()
         {
             var target = new Class2();
-
-            Func<WeakReference> setupBinding = () =>
-            {
-                var source = new Subject<string>();
-                var sub = target.Bind((AvaloniaProperty)Class1.FooProperty, source);
-                return new WeakReference(source);
-            };
-        
-            var weakSource = setupBinding();
+            var weakSource = SetupDirectBinding(target);
 
             Action completeSource = () =>
             {
@@ -455,6 +447,13 @@ namespace Avalonia.Base.UnitTests
             Assert.True(called);
         }
 
+        private WeakReference SetupDirectBinding(Class2 target)
+        {
+            var source = new Subject<string>();
+            var sub = target.Bind((AvaloniaProperty)Class1.FooProperty, source);
+            return new WeakReference(source);
+        }
+
         private class Class1 : AvaloniaObject
         {
             public static readonly DirectProperty<Class1, string> FooProperty =