- Address review comments from https://codereview.chromium.org/474913004/

runtime/vm/snapshot.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 VM_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 317 matching lines @@
       reference_ = other.reference_;
       state_ = other.state_;
       return *this;
     }
 
    private:
     Object* reference_;
     DeserializeState state_;
   };
 
-  PageSpace* old_space() { return old_space_; }
+  PageSpace* old_space() const { return old_space_; }
 
   // Allocate uninitialized objects, this is used when reading a full snapshot.
   RawObject* AllocateUninitialized(intptr_t class_id, intptr_t size);
 
   RawClass* ReadClassId(intptr_t object_id);
   RawObject* ReadObjectImpl();
   RawObject* ReadObjectImpl(intptr_t header);
   RawObject* ReadObjectRef();
 
   // Read a VM isolate object that was serialized as an Id.
@@ skipping 371 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_