Remove --harmony-tostring runtime flag

test/cctest/test-api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 13282 matching lines @@
       v8_compile("new Object()")->Run(context.local()).ToLocalChecked();
   value = object.As<v8::Object>()
               ->ObjectProtoToString(context.local())
               .ToLocalChecked();
   CHECK(value->IsString() &&
         value->Equals(context.local(), v8_str("[object Object]")).FromJust());
 }
 
 
 TEST(ObjectProtoToStringES6) {
-  // TODO(dslomov, caitp): merge into ObjectProtoToString test once shipped.
-  i::FLAG_harmony_tostring = true;
   LocalContext context;
   v8::Isolate* isolate = CcTest::isolate();
   v8::HandleScope scope(isolate);
   Local<v8::FunctionTemplate> templ = v8::FunctionTemplate::New(isolate);
   templ->SetClassName(v8_str("MyClass"));
 
   Local<String> customized_tostring = v8_str("customized toString");
 
   // Replace Object.prototype.toString
   CompileRun(
@@ skipping 11437 matching lines @@
   allowed_access = false;
   CompileRun("var result = [].concat(object)");
   ExpectTrue("Array.isArray(result)");
   ExpectTrue("result[0] === object");
   ExpectTrue("result.length === 1");
   ExpectTrue("object[Symbol.isConcatSpreadable] === undefined");
 }
 
 
 TEST(AccessCheckedToStringTag) {
-  i::FLAG_harmony_tostring = true;
   v8::Isolate* isolate = CcTest::isolate();
   HandleScope scope(isolate);
   LocalContext env;
 
   // Object with access check
   Local<ObjectTemplate> object_template = v8::ObjectTemplate::New(isolate);
   object_template->SetAccessCheckCallback(AccessBlocker);
   Local<Object> object =
       object_template->NewInstance(env.local()).ToLocalChecked();
 
@@ skipping 80 matching lines @@
   CHECK(proxy->GetTarget()->SameValue(target));
   CHECK(proxy->GetHandler()->SameValue(handler));
 
   proxy->Revoke();
   CHECK(proxy->IsProxy());
   CHECK(!target->IsProxy());
   CHECK(proxy->IsRevoked());
   CHECK(proxy->GetTarget()->SameValue(target));
   CHECK(proxy->GetHandler()->IsNull());
 }