Revert of Precisely determine Windows thread stack size.

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

Index: third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp
diff --git a/third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp b/third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp
index 345e71b1970e485f3dfb6fe7570097dc823e98ca..c118c814b2bdb23a966cb4aa70139e398bf593ea 100644
--- a/third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp
+++ b/third_party/WebKit/Source/platform/heap/StackFrameDepth.cpp
@@ -98,7 +98,14 @@
     // 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;