[runtime] Replace hidden_string with a 0-hash-code private symbol

src/objects-debug.cc

 // Copyright 2012 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/objects.h"
 
 #include "src/bootstrapper.h"
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/field-type.h"
@@ skipping 190 matching lines @@
 void HeapObject::VerifyHeapPointer(Object* p) {
   CHECK(p->IsHeapObject());
   HeapObject* ho = HeapObject::cast(p);
   CHECK(ho->GetHeap()->Contains(ho));
 }
 
 
 void Symbol::SymbolVerify() {
   CHECK(IsSymbol());
   CHECK(HasHashCode());
-  CHECK_GT(Hash(), 0u);
+  CHECK(GetHeap()->hidden_properties_symbol() == this || Hash() > 0u);
   CHECK(name()->IsUndefined() || name()->IsString());
 }
 
 
 void HeapNumber::HeapNumberVerify() {
   CHECK(IsHeapNumber() || IsMutableHeapNumber());
 }
 
 
 void Simd128Value::Simd128ValueVerify() { CHECK(IsSimd128Value()); }
@@ skipping 1098 matching lines @@
 
   // Both are done at the same time.
   CHECK_EQ(new_it.done(), old_it.done());
 }
 
 
 #endif  // DEBUG
 
 }  // namespace internal
 }  // namespace v8