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

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index ef3d461df1a415f7ca3a7702088d7e5d6cdb4310..0d01ec2f5b004446b66ec25dfc44be175f314bdc 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -208,7 +208,7 @@ void HeapObject::VerifyHeapPointer(Object* p) {
 void Symbol::SymbolVerify() {
   CHECK(IsSymbol());
   CHECK(HasHashCode());
-  CHECK_GT(Hash(), 0u);
+  CHECK(GetHeap()->hidden_properties_symbol() == this || Hash() > 0u);
   CHECK(name()->IsUndefined() || name()->IsString());
 }