Introduce object visitor to estimate the size of a native context.

src/context-measure.h

Index: src/context-measure.h
diff --git a/src/context-measure.h b/src/context-measure.h
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+++ b/src/context-measure.h
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+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_CONTEXT_MEASURE_H_
+#define V8_CONTEXT_MEASURE_H_
+
+#include "src/snapshot/serialize.h"
+
+namespace v8 {
+namespace internal {
+
+class ContextMeasure : public ObjectVisitor {
+ public:
+  explicit ContextMeasure(Context* context);
+
+  int Size() { return size_; }
+  int Count() { return count_; }
+
+  void VisitPointers(Object** start, Object** end);
+
+ private:
+  void MeasureObject(HeapObject* object);
+  void MeasureDeferredObjects();
+  void MeasureAndRecurse(HeapObject* object);
+  bool IsShared(HeapObject* object);
+
+  Context* context_;
+
+  BackReferenceMap back_reference_map_;
+  RootIndexMap root_index_map_;
+
+  static const int kMaxRecursion = 16;
+  int recursion_depth_;
+  List<HeapObject*> deferred_objects_;
+
+  int count_;
+  int size_;
+
+  DisallowHeapAllocation no_gc_;
+
+  DISALLOW_COPY_AND_ASSIGN(ContextMeasure);
+};
+}
+}  // namespace v8::internal
+
+#endif  // V8_CONTEXT_MEASURE_H_