Revert "Remove support for MSVC"

sky/engine/wtf/HashFunctions.h

 /*
  * Copyright (C) 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 106 matching lines @@
             return bitwise_cast<Bits>(a) == bitwise_cast<Bits>(b);
         }
         static const bool safeToCompareToEmptyOrDeleted = true;
     };
 
     // pointer identity hash function
 
     template<typename T> struct PtrHash {
         static unsigned hash(T key)
         {
+#if COMPILER(MSVC)
+#pragma warning(push)
+#pragma warning(disable: 4244) // work around what seems to be a bug in MSVC's conversion warnings
+#endif
             return IntHash<uintptr_t>::hash(reinterpret_cast<uintptr_t>(key));
+#if COMPILER(MSVC)
+#pragma warning(pop)
+#endif
         }
         static bool equal(T a, T b) { return a == b; }
         static bool equal(std::nullptr_t, T b) { return b == 0; }
         static bool equal(T a, std::nullptr_t) { return a == 0; }
         static const bool safeToCompareToEmptyOrDeleted = true;
     };
     template<typename P> struct PtrHash<RefPtr<P> > : PtrHash<P*> {
         using PtrHash<P*>::hash;
         static unsigned hash(const RefPtr<P>& key) { return hash(key.get()); }
         static unsigned hash(const PassRefPtr<P>& key) { return hash(key.get()); }
@@ skipping 53 matching lines @@
     // make IntHash the default hash function for many integer types
 
     template<> struct DefaultHash<short> { typedef IntHash<unsigned> Hash; };
     template<> struct DefaultHash<unsigned short> { typedef IntHash<unsigned> Hash; };
     template<> struct DefaultHash<int> { typedef IntHash<unsigned> Hash; };
     template<> struct DefaultHash<unsigned> { typedef IntHash<unsigned> Hash; };
     template<> struct DefaultHash<long> { typedef IntHash<unsigned long> Hash; };
     template<> struct DefaultHash<unsigned long> { typedef IntHash<unsigned long> Hash; };
     template<> struct DefaultHash<long long> { typedef IntHash<unsigned long long> Hash; };
     template<> struct DefaultHash<unsigned long long> { typedef IntHash<unsigned long long> Hash; };
+
+#if !COMPILER(MSVC) || defined(_NATIVE_WCHAR_T_DEFINED)
     template<> struct DefaultHash<wchar_t> { typedef IntHash<wchar_t> Hash; };
+#endif
+
     template<> struct DefaultHash<float> { typedef FloatHash<float> Hash; };
     template<> struct DefaultHash<double> { typedef FloatHash<double> Hash; };
 
     // make PtrHash the default hash function for pointer types that don't specialize
 
     template<typename P> struct DefaultHash<P*> { typedef PtrHash<P*> Hash; };
     template<typename P> struct DefaultHash<RefPtr<P> > { typedef PtrHash<RefPtr<P> > Hash; };
     template<typename P> struct DefaultHash<RawPtr<P> > { typedef PtrHash<RawPtr<P> > Hash; };
     template<typename P> struct DefaultHash<OwnPtr<P> > { typedef PtrHash<OwnPtr<P> > Hash; };
 
@@ skipping 20 matching lines @@
 
     template<typename T, typename U> struct DefaultHash<std::pair<T, U> > { typedef PairHash<T, U> Hash; };
 
 } // namespace WTF
 
 using WTF::DefaultHash;
 using WTF::IntHash;
 using WTF::PtrHash;
 
 #endif // WTF_HashFunctions_h