Create read only handles for empty_array and sentinel objects

vm/handles.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_HANDLES_H_
 #define VM_HANDLES_H_
 
 #include "vm/allocation.h"
 #include "vm/flags.h"
 
@@ skipping 218 matching lines @@
   void ZapFreeScopedHandles();
 #endif
 
   HandlesBlock* zone_blocks_;  // List of zone handles.
   HandlesBlock first_scoped_block_;  // First block of scoped handles.
   HandlesBlock* scoped_blocks_;  // List of scoped handles.
   // Last block visited by VisitUnvisitedHandles.
   HandlesBlock* last_visited_block_;
 
   friend class HandleScope;
-  friend class Symbols;
+  friend class Dart;
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Handles);
 };
 
 
 static const int kVMHandleSizeInWords = 2;
 static const int kVMHandlesPerChunk = 64;
 static const int kOffsetOfRawPtr = kWordSize;
 class VMHandles : public Handles<kVMHandleSizeInWords,
                                  kVMHandlesPerChunk,
@@ skipping 89 matching lines @@
 };
 #endif  // defined(DEBUG)
 
 // Macro to start a no handles scope in the code.
 #define NOHANDLESCOPE(isolate)                                                \
     dart::NoHandleScope no_vm_internal_handles_scope_(isolate);
 
 }  // namespace dart
 
 #endif  // VM_HANDLES_H_