Keep shadow stacks to help heap checker unwind without frame pointers

third_party/tcmalloc/chromium/src/linux_shadow_stacks.h

Index: third_party/tcmalloc/chromium/src/linux_shadow_stacks.h
===================================================================
--- third_party/tcmalloc/chromium/src/linux_shadow_stacks.h	(revision 0)
+++ third_party/tcmalloc/chromium/src/linux_shadow_stacks.h	(revision 0)
@@ -0,0 +1,20 @@
+// Copyright (c) 2006-2010 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 THIRD_PARTY_TCMALLOC_CHROMIUM_SRC_LINUX_SHADOW_STACKS_H__
+#define THIRD_PARTY_TCMALLOC_CHROMIUM_SRC_LINUX_SHADOW_STACKS_H__
+
+#define NO_INSTRUMENT __attribute__((no_instrument_function))
+
+extern "C" {
+void init()  NO_INSTRUMENT;
+void __cyg_profile_func_enter(void *this_fn, void *call_site)  NO_INSTRUMENT;
+void __cyg_profile_func_exit(void *this_fn, void *call_site)  NO_INSTRUMENT;
+void *get_shadow_ip_stack(int *index /*OUT*/) NO_INSTRUMENT;
+void *get_shadow_sp_stack(int *index /*OUT*/) NO_INSTRUMENT;
+}
+
+#undef NO_INSTRUMENT
+
+#endif  // THIRD_PARTY_TCMALLOC_CHROMIUM_SRC_LINUX_SHADOW_STACKS_H__