[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_string_deduplicator.h

+// Copyright 2017 The Chromium 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 BASE_TRACE_EVENT_HEAP_PROFILER_STRING_DEDUPLICATOR_H_
+#define BASE_TRACE_EVENT_HEAP_PROFILER_STRING_DEDUPLICATOR_H_
+
+#include <deque>
+#include <string>
+#include <unordered_map>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/strings/string_piece.h"
+
+namespace base {
+namespace trace_event {
+
+class TraceEventMemoryOverhead;
+class TracedValue;
+
+// Data structure that assigns a unique numeric ID to |const char*|s.
+class BASE_EXPORT StringDeduplicator {
+ public:
+  StringDeduplicator();
+  ~StringDeduplicator();
+
+  // Inserts a string and returns its ID.
+  int Insert(StringPiece string);
+
+  // Append {ID -> string} mappings that were added after the last call
+  // to this function.
+  void SerializeIncrementally(TracedValue* traced_value);
+
+  // Estimates memory overhead including |sizeof(StringDeduplicator)|.
+  void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead);
+
+ private:
+  // StringPieces in the map reference values from |string_|.
+  std::unordered_map<StringPiece, int, StringPieceHash> string_ids_;
+  std::deque<std::string> strings_;
+  size_t last_serialized_index_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringDeduplicator);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_HEAP_PROFILER_STRING_DEDUPLICATOR_H_