ES6 symbols: fix corner cases of equality operators

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 5c848800b37ab8ad90da48b05ba6c022db18f494..54c5238a01927dc7b7adba59e951893579bdb445 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2504,7 +2504,10 @@ void Name::set_hash_field(uint32_t value) {
 
 bool Name::Equals(Name* other) {
   if (other == this) return true;
-  if (this->IsUniqueName() && other->IsUniqueName()) return false;
+  if (this->IsSymbol() || other->IsSymbol() ||
+      (this->IsInternalizedString() && other->IsInternalizedString())) {
+    return false;
+  }
   return String::cast(this)->SlowEquals(String::cast(other));
 }