Move the canonical empty context to the VM isolate.

runtime/vm/raw_object.h

 // 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.
 
 #ifndef RUNTIME_VM_RAW_OBJECT_H_
 #define RUNTIME_VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/atomic.h"
 #include "vm/exceptions.h"
@@ skipping 1420 matching lines @@
   RawObject** from() { return reinterpret_cast<RawObject**>(&ptr()->parent_); }
   RawContext* parent_;
 
   // Variable length data follows here.
   RawObject** data() { OPEN_ARRAY_START(RawObject*, RawObject*); }
   RawObject* const* data() const { OPEN_ARRAY_START(RawObject*, RawObject*); }
   RawObject** to(intptr_t num_vars) {
     return reinterpret_cast<RawObject**>(&ptr()->data()[num_vars - 1]);
   }
 
+  friend class Object;
   friend class SnapshotReader;
 };
 
 
 class RawContextScope : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ContextScope);
 
   // TODO(iposva): Switch to conventional enum offset based structure to avoid
   // alignment mishaps.
   struct VariableDesc {
@@ skipping 983 matching lines @@
   COMPILE_ASSERT(kExternalTypedDataInt8ArrayCid ==
                  kTypedDataInt8ArrayViewCid + 15);
   COMPILE_ASSERT(kByteBufferCid == kExternalTypedDataInt8ArrayCid + 14);
   COMPILE_ASSERT(kNullCid == kByteBufferCid + 1);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_RAW_OBJECT_H_