Implement ES2015 class feature (part I.) (#2404)

This patch is the first milestone of the implementation of this new language element.

Currently supported:
 - Class statement
 - Class expression
 - Static methods

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/parser/js/js-parser-util.c

@@ -920,6 +920,20 @@ parser_error_to_string (parser_error_t error) /**< error code */
       return "Expected '}' token.";
     }
 #endif /* !CONFIG_DISABLE_ES2015_TEMPLATE_STRINGS */
+#ifndef CONFIG_DISABLE_ES2015_CLASS
+    case PARSER_ERR_MULTIPLE_CLASS_CONSTRUCTOR:
+    {
+      return "Multiple constructors are not allowed.";
+    }
+    case PARSER_ERR_CLASS_CONSTRUCTOR_AS_ACCESSOR:
+    {
+      return "Class constructor may not be an accessor.";
+    }
+    case PARSER_ERR_CLASS_STATIC_PROPERTY_NAME_PROTOTYPE:
+    {
+      return "Classes may not have a static property called 'prototype'.";
+    }
+#endif /* !CONFIG_DISABLE_ES2015_CLASS */
     case PARSER_ERR_COLON_EXPECTED:
     {
       return "Expected ':' token.";