Create read only handles for empty_array and sentinel objects

vm/snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/exceptions.h"
@@ skipping 638 matching lines @@
 }
 
 
 RawObject* SnapshotReader::ReadVMIsolateObject(intptr_t header_value) {
   intptr_t object_id = GetVMIsolateObjectId(header_value);
   if (object_id == kNullObject) {
     // This is a singleton null object, return it.
     return Object::null();
   }
   if (object_id == kSentinelObject) {
-    return Object::sentinel();
+    return Object::sentinel().raw();
   }
   if (object_id == kEmptyArrayObject) {
-    return Object::empty_array();
+    return Object::empty_array().raw();
   }
   intptr_t class_id = ClassIdFromObjectId(object_id);
   if (IsSingletonClassId(class_id)) {
     return isolate()->class_table()->At(class_id);  // get singleton class.
   } else {
     ASSERT(Symbols::IsVMSymbolId(object_id));
     return Symbols::GetVMSymbol(object_id);  // return VM symbol.
   }
   UNREACHABLE();
   return Object::null();
@@ skipping 121 matching lines @@
 
 
 void SnapshotWriter::HandleVMIsolateObject(RawObject* rawobj) {
   // Check if it is a singleton null object.
   if (rawobj == Object::null()) {
     WriteVMIsolateObject(kNullObject);
     return;
   }
 
   // Check if it is a singleton sentinel object.
-  if (rawobj == Object::sentinel()) {
+  if (rawobj == Object::sentinel().raw()) {
     WriteVMIsolateObject(kSentinelObject);
     return;
   }
 
   // Check if it is a singleton empty array object.
-  if (rawobj == Object::empty_array()) {
+  if (rawobj == Object::empty_array().raw()) {
     WriteVMIsolateObject(kEmptyArrayObject);
     return;
   }
 
   // Check if it is a singleton class object which is shared by
   // all isolates.
   intptr_t id = rawobj->GetClassId();
   if (id == kClassCid) {
     RawClass* raw_class = reinterpret_cast<RawClass*>(rawobj);
     intptr_t class_id = raw_class->ptr()->id_;
@@ skipping 494 matching lines @@
     UnmarkAll();
     isolate->set_long_jump_base(base);
   } else {
     isolate->set_long_jump_base(base);
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart