Purge UnspecifiedBoolType from Blink.

third_party/WebKit/Source/bindings/core/v8/Nullable.h

 // Copyright 2014 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.
 
 #ifndef Nullable_h
 #define Nullable_h
 
 #include "platform/heap/Handle.h"
 #include "wtf/Assertions.h"
 
@@ skipping 47 matching lines @@
     void set(std::nullptr_t)
     {
         m_value = T();
         m_isNull = true;
     }
 
     const T& get() const { ASSERT(!m_isNull); return m_value; }
     T& get() { ASSERT(!m_isNull); return m_value; }
     bool isNull() const { return m_isNull; }
 
-    // See comment in RefPtr.h about what UnspecifiedBoolType is.
-    typedef const T* UnspecifiedBoolType;
-    operator UnspecifiedBoolType() const { return m_isNull ? 0 : &m_value; }
+    explicit operator bool() const { return !m_isNull; }
 
     bool operator==(const Nullable& other) const
     {
         return (m_isNull && other.m_isNull) || (!m_isNull && !other.m_isNull && m_value == other.m_value);
     }
 
     DEFINE_INLINE_TRACE()
     {
         TraceIfNeeded<T>::trace(visitor, m_value);
     }
 
 private:
     T m_value;
     bool m_isNull;
 };
 
 } // namespace blink
 
 #endif // Nullable_h