Add support for measure mode

src/csharp/Facebook.CSSLayout/CSSMeasureMode.cs

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+namespace Facebook.CSSLayout
+{
+    public enum CSSMeasureMode
+    {
+        Undefined,
+        Exactly,
+        AtMost,
+    }
+}