Getter for literal expression value

src/ol/expression/expressions.js

@@ -308,6 +308,15 @@ ol.expression.Literal.prototype.evaluate = function() {
 };
 
 
+/**
+ * Get the literal value.
+ * @return {string|number|boolean|null} The literal value.
+ */
+ol.expression.Literal.prototype.getValue = function() {
+  return this.value_;
+};
+
+
 /**
  * @enum {string}
  */