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.

Committed: http://code.google.com/p/v8/source/detail?r=4116

[Mads Ager (chromium), 2010-03-12 12:19:29]

LGTM

http://codereview.chromium.org/912002/diff/1/2
File src/ast.cc (right):

http://codereview.chromium.org/912002/diff/1/2#newcode558
src/ast.cc:558: // Booleans, void Undefined, typeof String (but host objects are
Let's remove the comment about host objects being implementation-dependents.  As
I read the spec, typeof returns a string which can be implementation dependent,
but all that matters here is that it *does* return a string.