Revert of Precisely determine Windows thread stack size.

third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp

 // Copyright 2015 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.
 
 #include "config.h"
 #include "platform/heap/StackFrameDepth.h"
 
 #include "public/platform/Platform.h"
 
 #if OS(WIN)
@@ skipping 80 matching lines @@
 #if OS(FREEBSD)
     pthread_attr_destroy(&attr);
 #endif
 
     return 0;
 #elif OS(MACOSX)
     // FIXME: pthread_get_stacksize_np() returns shorter size than actual stack
     // size for the main thread on Mavericks(10.9).
     return 0;
 #elif OS(WIN) && COMPILER(MSVC)
-    return ThreadState::current()->threadStackSize();
+    // On Windows stack limits for the current thread are available in
+    // the thread information block (TIB). Its fields can be accessed through
+    // FS segment register on x86 and GS segment register on x86_64.
+#ifdef _WIN64
+    return __readgsqword(offsetof(NT_TIB64, StackBase)) - __readgsqword(offsetof(NT_TIB64, StackLimit));
+#else
+    return __readfsdword(offsetof(NT_TIB, StackBase)) - __readfsdword(offsetof(NT_TIB, StackLimit));
+#endif
 #else
 #error "Stack frame size estimation not supported on this platform."
     return 0;
 #endif
 }
 
 void* StackFrameDepth::getStackStart()
 {
 #if defined(__GLIBC__) || OS(ANDROID) || OS(FREEBSD)
     pthread_attr_t attr;
@@ skipping 35 matching lines @@
     return reinterpret_cast<void*>(__readgsqword(offsetof(NT_TIB64, StackBase)));
 #else
     return reinterpret_cast<void*>(__readfsdword(offsetof(NT_TIB, StackBase)));
 #endif
 #else
 #error Unsupported getStackStart on this platform.
 #endif
 }
 
 } // namespace blink