[Mojo] Make javascript enums extensible.

mojo/public/js/validator.js

Index: mojo/public/js/validator.js
diff --git a/mojo/public/js/validator.js b/mojo/public/js/validator.js
index cbf7521b5c3bfa4717a500ee53836342d4a6fc5b..bd0a4310253d230a1670599ee25f013c30739295 100644
--- a/mojo/public/js/validator.js
+++ b/mojo/public/js/validator.js
@@ -24,10 +24,15 @@ define("mojo/public/js/validator", [
         'VALIDATION_ERROR_DIFFERENT_SIZED_ARRAYS_IN_MAP',
     INVALID_UNION_SIZE: 'VALIDATION_ERROR_INVALID_UNION_SIZE',
     UNEXPECTED_NULL_UNION: 'VALIDATION_ERROR_UNEXPECTED_NULL_UNION',
+    UNKNOWN_ENUM_VALUE: 'VALIDATION_ERROR_UNKNOWN_ENUM_VALUE',
   };
 
   var NULL_MOJO_POINTER = "NULL_MOJO_POINTER";
 
+  function isEnumClass(cls) {
+    return typeof cls.isKnownEnumValue === 'function';
+  }
+
   function isStringClass(cls) {
     return cls === codec.String || cls === codec.NullableString;
   }
@@ -98,6 +103,13 @@ define("mojo/public/js/validator", [
     return true;
   }
 
+  Validator.prototype.validateEnum = function(offset, enumClass, nullable) {
+    // Note: Assumes that enums are always 32 bits! But this matches
+    // mojom::generate::pack::PackedField::GetSizeForKind, so it should be okay.
+    var value = this.message.buffer.getInt32(offset);
+    return enumClass.validate(value);
+  }
+
   Validator.prototype.validateHandle = function(offset, nullable) {
     var index = this.message.buffer.getUint32(offset);
 
@@ -347,6 +359,8 @@ define("mojo/public/js/validator", [
       return this.validateArrayElements(
           elementsOffset, numElements, elementType.cls, nullable,
           expectedDimensionSizes, currentDimension + 1);
+    if (isEnumClass(elementType))
+      return this.validateEnum(elementsOffset, elementType, nullable);
 
     return validationError.NONE;
   }