https://bugs.webkit.org/show_bug.cgi?id=120314

Reviewed by Darin Adler.

Currently with the way that defineProperty works, we leave a stray low bit set in 
PropertyDescriptor::m_attributes in the following code:

var o = {};
Object.defineProperty(o, 100, {writable:true, enumerable:true, configurable:true, value:"foo"});
        
This is due to the fact that the lowest non-zero attribute (ReadOnly) is represented as 1 << 1 
instead of 1 << 0. We then calculate the default attributes as (DontDelete << 1) - 1, which is 0xF, 
but only the top three bits mean anything. Even in the case above, the top three bits are set 
to 0 but the bottom bit remains set, which causes us to think m_attributes is non-zero.

Since some of these attributes and their corresponding values are exposed in the JavaScriptCore 
framework's public C API, it's safer to just change how we calculate the default value, which is
where the weirdness was originating from in the first place.

* runtime/PropertyDescriptor.cpp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154630 268f45cc-cd09-0410-ab3c-d52691b4dbfc