Put ThinStrings behind a flag (off by default)

test/cctest/test-code-stub-assembler.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/utils/random-number-generator.h"
 #include "src/builtins/builtins-promise.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/compiler/node.h"
 #include "src/isolate.h"
@@ skipping 295 matching lines @@
     CHECK(!key->HasHashCode());
     ft.CheckTrue(key, expect_bailout);
   }
 
   {
     // TryToName(<non-internalized string>) => bailout.
     Handle<Object> key = isolate->factory()->NewStringFromAsciiChecked("test");
     ft.CheckTrue(key, expect_bailout);
   }
 
-  {
+  if (FLAG_thin_strings) {
     // TryToName(<thin string>) => internalized version.
     Handle<String> s = isolate->factory()->NewStringFromAsciiChecked("foo");
     Handle<String> internalized = isolate->factory()->InternalizeString(s);
     ft.CheckTrue(s, expect_unique, internalized);
   }
 
-  {
+  if (FLAG_thin_strings) {
     // TryToName(<thin two-byte string>) => internalized version.
     uc16 array1[] = {2001, 2002, 2003};
     Vector<const uc16> str1(array1);
     Handle<String> s =
         isolate->factory()->NewStringFromTwoByte(str1).ToHandleChecked();
     Handle<String> internalized = isolate->factory()->InternalizeString(s);
     ft.CheckTrue(s, expect_unique, internalized);
   }
 }
 
@@ skipping 2121 matching lines @@
   m.Return(m.SmiConstant(0));
 
   Handle<Code> code = data.GenerateCode();
   CHECK(!code.is_null());
   FunctionTester ft(code, kNumParams);
   CHECK_EQ(1, Handle<Smi>::cast(ft.Call().ToHandleChecked())->value());
 }
 
 }  // namespace internal
 }  // namespace v8