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diff --git a/third_party/base/debug/alias.h b/third_party/base/debug/alias.h
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+++ b/third_party/base/debug/alias.h
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+// Copyright (c) 2011 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_DEBUG_ALIAS_H_
+#define BASE_DEBUG_ALIAS_H_
+
+namespace base {
+namespace debug {
+
+// Make the optimizer think that var is aliased. This is to prevent it from
+// optimizing out local variables that would not otherwise be live at the point
+// of a potential crash.
+// base::debug::Alias should only be used for local variables, not globals,
+// object members, or function return values - these must be copied to locals if
+// you want to ensure they are recorded in crash dumps.
+// Note that if the local variable is a pointer then its value will be retained
+// but the memory that it points to will probably not be saved in the crash
+// dump - by default only stack memory is saved. Therefore the aliasing
+// technique is usually only worthwhile with non-pointer variables. If you have
+// a pointer to an object and you want to retain the object's state you need to
+// copy the object or its fields to local variables. Example usage:
+//   int last_error = err_;
+//   base::debug::Alias(&last_error);
+//   DEBUG_ALIAS_FOR_CSTR(name_copy, p->name, 16);
+//   CHECK(false);
+void Alias(const void* var);
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_ALIAS_H_