Allows gen_snapshot to be built with asan in the Mojo tree.

runtime/bin/address_sanitizer.cc

Index: runtime/bin/address_sanitizer.cc
===================================================================
--- runtime/bin/address_sanitizer.cc	(revision 0)
+++ runtime/bin/address_sanitizer.cc	(working copy)
@@ -0,0 +1,27 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "platform/globals.h"
+
+#if defined(TARGET_OS_LINUX) || defined(TARGET_OS_MACOSX)
+#if defined(__has_feature)
+#if __has_feature(address_sanitizer)
+
+const char *kAsanDefaultOptions =
+    "strict_memcmp=0 symbolize=0 check_printf=1 use_sigaltstack=1 "
+    "detect_leaks=0 fast_unwind_on_fatal=1 handle_segv=0 ";
+
+extern "C"
+__attribute__((no_sanitize_address))
+__attribute__((visibility("default")))
+// The function isn't referenced from the executable itself. Make sure it isn't
+// stripped by the linker.
+__attribute__((used))
+const char *__asan_default_options() {
+  return kAsanDefaultOptions;
+}
+
+#endif  // __has_feature(address_sanitizer)
+#endif  // defined(__has_feature)
+#endif  //  defined(TARGET_OS_LINUX) || defined(TARGET_OS_MACOSX)