Add num.sign getter.

Add num.sign getter.

BUG= http://dartbug.com/15580
R=sgjesse@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31126

[Søren Gjesse, 2013-12-13 11:45:04]

lgtm

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
File sdk/lib/_internal/lib/js_number.dart (right):

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
sdk/lib/_internal/lib/js_number.dart:62: num get sign => this > 0 ? 1 : this < 0
? -1 : this;
EcmaScript 6 has Math.sign with the same semantics
(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Obje...),
but I guess we don't want to check whether that exists.

[Lasse Reichstein Nielsen, 2013-12-13 12:08:47]

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
File sdk/lib/_internal/lib/js_number.dart (right):

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
sdk/lib/_internal/lib/js_number.dart:62: num get sign => this > 0 ? 1 : this < 0
? -1 : this;
Interesting. Did not know that.
Since it most likely doesn't exist yet, I don't think we'd want to use that any
time soon. When ES6 gets closer to finished, and implementations become ready,
we might want to look at it again.

We definitely don't want to test for existence every time, so it would be
something to do during startup.

[Lasse Reichstein Nielsen, 2013-12-13 12:10:37]

Committed patchset #2 manually as r31126 (presubmit successful).

[sra1, 2014-03-07 00:53:34]

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
File sdk/lib/_internal/lib/js_number.dart (right):

https://codereview.chromium.org/113833002/diff/20001/sdk/lib/_internal/lib/js...
sdk/lib/_internal/lib/js_number.dart:245: if (false)
_shrReceiverPositive(other);
What is the purpose of this dead code?
Please delete it or explain it.