[Isolates] Avoid dereferencing Isolate::Current() to check oddball identities...

src/handles.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 64 matching lines @@
            reinterpret_cast<Address>(*location_) != kZapValue);
     return location_;
   }
 
   template <class S> static Handle<T> cast(Handle<S> that) {
     T::cast(*that);
     return Handle<T>(reinterpret_cast<T**>(that.location()));
   }
 
   static Handle<T> null() { return Handle<T>(); }
-  bool is_null() { return location_ == NULL; }
+  bool is_null() const { return location_ == NULL; }
 
   // Closes the given scope, but lets this handle escape. See
   // implementation in api.h.
   inline Handle<T> EscapeFrom(v8::HandleScope* scope);
 
  private:
   T** location_;
 };
 
 
@@ skipping 263 matching lines @@
  private:
   bool has_been_transformed_;  // Tells whether the object has been transformed.
   int unused_property_fields_;  // Captures the unused number of field.
   Handle<JSObject> object_;    // The object being optimized.
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_