Add a predicate IsPrimitive to AST Expression nodes.

Add a predicate IsPrimitive to AST Expression nodes.

IsPrimitive reflects that an expression's value is known statically to
be one of the ECMA-262-3 JS types other than Object (e.g., Undefined,
Null, Boolean, String, or Number).

The type conversions ToPrimitive, ToNumber, ToInteger, ToInt32,
ToUInt32, ToUint16, ToString, or ToObject cannot invoke user code for
primitive input values.  ToObject throws a TypeError if its input is
Undefined or Null.

Review URL: http://codereview.chromium.org/912002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4116 ce2b1a6d-e550-0410-aec6-3dcde31c8c00