Add guard pages in front of platform allocations

src/platform-win32.cc

Index: src/platform-win32.cc
===================================================================
--- src/platform-win32.cc	(revision 8679)
+++ src/platform-win32.cc	(working copy)
@@ -957,6 +957,12 @@
 }
 
 
+void OS::Guard(void* address, const size_t size) {
+  DWORD oldprotect;
+  VirtualProtect(address, size, PAGE_READONLY | PAGE_GUARD, &oldprotect);
+}
+
+
 void OS::Sleep(int milliseconds) {
   ::Sleep(milliseconds);
 }