Add support for storage type to base::Flags.

src/base/flags.h

 // Copyright 2014 the V8 project 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 V8_BASE_FLAGS_H_
 #define V8_BASE_FLAGS_H_
 
 #include "include/v8config.h"
 
 namespace v8 {
 namespace base {
 
 // The Flags class provides a type-safe way of storing OR-combinations of enum
-// values. The Flags<T> class is a template class, where T is an enum type.
+// values. The Flags<T, S> class is a template class, where T is an enum type,
+// and S is the underlying storage type (usually int).
 //
 // The traditional C++ approach for storing OR-combinations of enum values is to
 // use an int or unsigned int variable. The inconvenience with this approach is
 // that there's no type checking at all; any enum value can be OR'd with any
 // other enum value and passed on to a function that takes an int or unsigned
 // int.
-template <typename T>
+template <typename T, typename S = int>
 class Flags V8_FINAL {
  public:
   typedef T flag_type;
-  typedef int mask_type;
+  typedef S mask_type;
 
   Flags() : mask_(0) {}
   Flags(flag_type flag) : mask_(flag) {}  // NOLINT(runtime/explicit)
   explicit Flags(mask_type mask) : mask_(mask) {}
 
   Flags& operator&=(const Flags& flags) {
     mask_ &= flags.mask_;
     return *this;
   }
   Flags& operator|=(const Flags& flags) {
@@ skipping 20 matching lines @@
   Flags operator~() const { return Flags(~mask_); }
 
   operator mask_type() const { return mask_; }
   bool operator!() const { return !mask_; }
 
  private:
   mask_type mask_;
 };
 
 
-#define DEFINE_FLAGS(Type, Enum) typedef ::v8::base::Flags<Enum> Type
-
 #define DEFINE_OPERATORS_FOR_FLAGS(Type)                                       \
   inline ::v8::base::Flags<Type::flag_type> operator&(                         \
       Type::flag_type lhs,                                                     \
       Type::flag_type rhs)V8_UNUSED V8_WARN_UNUSED_RESULT;                     \
   inline ::v8::base::Flags<Type::flag_type> operator&(Type::flag_type lhs,     \
                                                       Type::flag_type rhs) {   \
     return ::v8::base::Flags<Type::flag_type>(lhs) & rhs;                      \
   }                                                                            \
   inline ::v8::base::Flags<Type::flag_type> operator&(                         \
       Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs)      \
@@ skipping 33 matching lines @@
   inline ::v8::base::Flags<Type::flag_type> operator^(                         \
       Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs) {    \
     return rhs ^ lhs;                                                          \
   } inline void operator^(Type::flag_type lhs, Type::mask_type rhs) V8_UNUSED; \
   inline void operator^(Type::flag_type lhs, Type::mask_type rhs) {}
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_FLAGS_H_