Fix undo on fields with validators with side effects.

core/events.js

@@ -550,6 +550,10 @@ Blockly.Events.Change.prototype.run = function(forward) {
     case 'field':
       var field = block.getField(this.name);
       if (field) {
+        // Run the validator for any side-effects it may have.
+        // The validator's opinion on validity is ignored.
+        var validator = field.getValidator();
+        validator && validator.call(field, value);
         field.setValue(value);
       } else {
         console.warn("Can't set non-existant field: " + this.name);

core/field.js

@@ -232,6 +232,14 @@ Blockly.Field.prototype.setValidator = function(handler) {
   this.validator_ = handler;
 };
 
+/**
+ * Gets the validation function for editable fields.
+ * @return {Function} Validation function, or null.
+ */
+Blockly.Field.prototype.getValidator = function() {
+  return this.validator_;
+};
+
 /**
  * Gets the group element for this editable field.
  * Used for measuring the size and for positioning.