ES6 symbols: turn symbols into a proper primitive type

ES6 symbols: turn symbols into a proper primitive type

(qua last week's TC39)

Specifically:
- Install Symbol constructor function on the global object.
- Adjust code generation for typeof.
- Remove IsSymbol built-in, IS_SYMBOL macro now defined using typeof.
- Remove hack that allowed symbols as constructor results, and some other special cases.
- Remove symbol_delegate and GetDelegate function.
- Extend ToBoolean stub to handle symbols.
- Extend ToNumber to return NaN on symbols.
- Poison symbol's toString function, and thereby ToString on symbols.

R=mstarzinger@chromium.org
BUG=v8:2158
Committed: http://code.google.com/p/v8/source/detail?r=14051

[Michael Starzinger, 2013-03-22 11:39:04]

LGTM if comments are addressed.

https://codereview.chromium.org/12957004/diff/1/src/bootstrapper.cc
File src/bootstrapper.cc (right):

https://codereview.chromium.org/12957004/diff/1/src/bootstrapper.cc#newcode1288
src/bootstrapper.cc:1288: factory()->NewJSObject(isolate()->object_function(),
TENURED);
This creates a new object for the prototype of the Symbol function. Is this
intended? I think it should be isolate->initial_object_prototype() instead. It
might make sense to add test coverage for that.

https://codereview.chromium.org/12957004/diff/1/src/contexts.h
File src/contexts.h (right):

https://codereview.chromium.org/12957004/diff/1/src/contexts.h#newcode291
src/contexts.h:291: SYMBOL_DELEGATE_INDEX,
Is this index still used? If not, let's drop it.

https://codereview.chromium.org/12957004/diff/1/src/symbol.js
File src/symbol.js (right):

https://codereview.chromium.org/12957004/diff/1/src/symbol.js#newcode42
src/symbol.js:42: throw new $TypeError("Symbol.prototype.toString is not
allowed");
See comments below about MakeTypeError, maybe you can find a message that suits
this error or you might have to add a new one.

https://codereview.chromium.org/12957004/diff/1/src/symbol.js#newcode49
src/symbol.js:49: throw new $TypeError("Symbol.prototype.valueOf is not
generic");
Use the following to generate the TypeError instead. This allows us to have one
single choke-point where all error objects and messages are generated.

throw MakeTypeError('incompatible_method_receiver',
                    ['Symbol.prototype.valueOf', this]);

[rossberg, 2013-03-22 12:37:44]

https://codereview.chromium.org/12957004/diff/1/src/bootstrapper.cc
File src/bootstrapper.cc (right):

https://codereview.chromium.org/12957004/diff/1/src/bootstrapper.cc#newcode1288
src/bootstrapper.cc:1288: factory()->NewJSObject(isolate()->object_function(),
TENURED);
On 2013/03/22 11:39:04, Michael Starzinger wrote:
> This creates a new object for the prototype of the Symbol function. Is this
> intended? I think it should be isolate->initial_object_prototype() instead. It
> might make sense to add test coverage for that.

Done.

https://codereview.chromium.org/12957004/diff/1/src/contexts.h
File src/contexts.h (right):

https://codereview.chromium.org/12957004/diff/1/src/contexts.h#newcode291
src/contexts.h:291: SYMBOL_DELEGATE_INDEX,
On 2013/03/22 11:39:04, Michael Starzinger wrote:
> Is this index still used? If not, let's drop it.

Good catch, done.

https://codereview.chromium.org/12957004/diff/1/src/symbol.js
File src/symbol.js (right):

https://codereview.chromium.org/12957004/diff/1/src/symbol.js#newcode42
src/symbol.js:42: throw new $TypeError("Symbol.prototype.toString is not
allowed");
On 2013/03/22 11:39:04, Michael Starzinger wrote:
> See comments below about MakeTypeError, maybe you can find a message that
suits
> this error or you might have to add a new one.

Done.

https://codereview.chromium.org/12957004/diff/1/src/symbol.js#newcode49
src/symbol.js:49: throw new $TypeError("Symbol.prototype.valueOf is not
generic");
On 2013/03/22 11:39:04, Michael Starzinger wrote:
> Use the following to generate the TypeError instead. This allows us to have
one
> single choke-point where all error objects and messages are generated.
> 
> throw MakeTypeError('incompatible_method_receiver',
>                     ['Symbol.prototype.valueOf', this]);

Done.