Implemented an averaging object histogram in the vm.

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 VM_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 425 matching lines @@
   friend class Api;
   friend class Array;
   friend class FreeListElement;
   friend class GCMarker;
   friend class ExternalTypedData;
   friend class Heap;
   friend class HeapProfiler;
   friend class HeapProfilerRootVisitor;
   friend class MarkingVisitor;
   friend class Object;
+  friend class ObjectHistogram;
   friend class RawExternalTypedData;
   friend class RawInstructions;
   friend class RawInstance;
   friend class RawTypedData;
   friend class Scavenger;
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class String;
   friend class TypedData;
   friend class TypedDataView;
@@ skipping 1231 matching lines @@
   // Make sure this is updated when new TypedData types are added.
   ASSERT(kTypedDataInt8ArrayViewCid == kTypedDataInt8ArrayCid + 12);
   ASSERT(kExternalTypedDataInt8ArrayCid == kTypedDataInt8ArrayViewCid + 13);
   ASSERT(kNullCid == kExternalTypedDataInt8ArrayCid + 12);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_