Bump to v4.0.0.

internal/cloneSymbol.js

@@ -0,0 +1,22 @@
+define(['./_Symbol'], function(_Symbol) {
+
+  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
+  var undefined;
+
+  /** Used to convert symbols to primitives and strings. */
+  var symbolProto = _Symbol ? _Symbol.prototype : undefined,
+      symbolValueOf = _Symbol ? symbolProto.valueOf : undefined;
+
+  /**
+   * Creates a clone of the `symbol` object.
+   *
+   * @private
+   * @param {Object} symbol The symbol object to clone.
+   * @returns {Object} Returns the cloned symbol object.
+   */
+  function cloneSymbol(symbol) {
+    return _Symbol ? Object(symbolValueOf.call(symbol)) : {};
+  }
+
+  return cloneSymbol;
+});