Turn off support for String + operator in the VM

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/flags.h"
 #include "vm/growable_array.h"
 #include "vm/longjump.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/resolver.h"
 #include "vm/scopes.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, enable_asserts, false, "Enable assert statements.");
 DEFINE_FLAG(bool, enable_type_checks, false, "Enable type checks.");
 DEFINE_FLAG(bool, trace_parser, false, "Trace parser operations.");
 DEFINE_FLAG(bool, warning_as_error, false, "Treat warnings as errors.");
 DEFINE_FLAG(bool, silent_warnings, false, "Silence warnings.");
-DEFINE_FLAG(bool, allow_string_plus, true, "Allow + operator on strings.");
+DEFINE_FLAG(bool, allow_string_plus, false, "Allow + operator on strings.");
 
 static void CheckedModeHandler(bool value) {
   FLAG_enable_asserts = value;
   FLAG_enable_type_checks = value;
 }
 
 DEFINE_FLAG_HANDLER(CheckedModeHandler,
                     enable_checked_mode,
                     "Enabled checked mode.");
 
@@ skipping 8547 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart