Add out-of-process memory logging stream parsing.

chrome/profiling/backtrace.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 CHROME_PROFILING_BACKTRACE_H_
+#define CHROME_PROFILING_BACKTRACE_H_
+
+#include <functional>
+#include <vector>
+
+#include "base/macros.h"
+#include "chrome/profiling/address.h"
+
+namespace profiling {
+
+// Holds a move-only stack backtrace and a precomputed hash. This backtrace
+// uses addresses in the instrumented process. This is in contrast to
+// base::StackTrace which is for getting and working with stack traces in the
+// current process.
+//
+// This is immutable since we assume it can be read from multiple threads
+// without locking.
+//
+// This class has a ref_count member which is used by the allocation tracker
+// to track references to the stack. The reference counting is managed
+// externally. Tracking live objects with a global atom list in a threadsafe
+// manner is much more difficult if this class derives from RefCount.
+class Backtrace {
+ public:
+  // Move-only class. Backtraces should be managed by BacktraceStorage and
+  // we shouldn't be copying vectors around.
+  explicit Backtrace(std::vector<Address>&& a);
+  Backtrace(Backtrace&& other) noexcept;
+  ~Backtrace();
+
+  Backtrace& operator=(Backtrace&& other);
+
+  bool operator==(const Backtrace& other) const;
+  bool operator!=(const Backtrace& other) const;
+
+  const std::vector<Address>& addrs() const;
+
+  size_t fingerprint() const { return fingerprint_; }
+
+ private:
+  friend class BacktraceStorage;  // Only BacktraceStorage can do ref counting.
+
+  // The reference counting is not threadsafe. it's assumed the
+  // BacktraceStorage is the only class accessing this, and it's done inside a
+  // lock.
+  void AddRef() const { ref_count_++; }
+  bool Release() const {  // Returns whether the result is non-zero.
+    return !!(--ref_count_);
+  }
+
+  std::vector<Address> addrs_;
+  size_t fingerprint_;
+  mutable int ref_count_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(Backtrace);
+};
+
+}  // namespace profiling
+
+namespace std {
+
+template <>
+struct hash<profiling::Backtrace> {
+  using argument_type = profiling::Backtrace;
+  using result_type = size_t;
+  result_type operator()(const argument_type& s) const {
+    return s.fingerprint();
+  }
+};
+
+}  // namespace std
+
+#endif  // CHROME_PROFILING_BACKTRACE_H_