Fast path for ThreadSpecific for main thread on TLS-slow platforms

third_party/WebKit/Source/wtf/StackUtil.h

Index: third_party/WebKit/Source/wtf/StackUtil.h
diff --git a/third_party/WebKit/Source/wtf/StackUtil.h b/third_party/WebKit/Source/wtf/StackUtil.h
new file mode 100644
index 0000000000000000000000000000000000000000..d99e8873241a82436124403cbbccfa14dd71d827
--- /dev/null
+++ b/third_party/WebKit/Source/wtf/StackUtil.h
@@ -0,0 +1,19 @@
+// 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 StackUtil_h
+#define StackUtil_h
+
+#include "wtf/WTFExport.h"
+#include <cstddef>
+#include <stdint.h>
+
+namespace WTF {
+
+WTF_EXPORT size_t getUnderestimatedStackSize();
+WTF_EXPORT void* getStackStart();
+
+}  // namespace WTF
+
+#endif  // StackUtil_h