Create _RootZone and _RootSpecification.

Create _RootZone and _RootSpecification.

R=lrn@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28641

[floitsch, 2013-10-15 11:56:32]

Should make the root-zone more efficient.
Also makes it easier to see if we forgot to update the root-zone for one of the
handlers.
And finally it should help dart2js which doesn't need to closurize everything if
nobody every calls it.

[Lasse Reichstein Nielsen, 2013-10-15 12:04:07]

lgtm

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart
File sdk/lib/async/zone.dart (right):

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart#newco...
sdk/lib/async/zone.dart:747: Map<Symbol, dynamic> copiedMap = new HashMap();
Why was the zoneValues based on Symbols only?
I see no problem using any kind of key.

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart#newco...
sdk/lib/async/zone.dart:783: : super(null, const _RootZoneSpecification(), const
<Symbol, dynamic>{});
Can you replace the map with null, since it is never read?

You override ... 15 out of 22 methods. 
Are you sure it wouldn't be easier to implement Zone and do the remaining five,
instead of passing irrelevant data to the super constructor.

[floitsch, 2013-10-15 12:47:21]

PTAL.

[Lasse Reichstein Nielsen, 2013-10-15 12:48:26]

lgtm

[floitsch, 2013-10-15 13:06:06]

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart
File sdk/lib/async/zone.dart (right):

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart#newco...
sdk/lib/async/zone.dart:747: Map<Symbol, dynamic> copiedMap = new HashMap();
On 2013/10/15 12:04:07, Lasse Reichstein Nielsen wrote:
> Why was the zoneValues based on Symbols only?
> I see no problem using any kind of key.

We can change later.

https://codereview.chromium.org/26151004/diff/1/sdk/lib/async/zone.dart#newco...
sdk/lib/async/zone.dart:783: : super(null, const _RootZoneSpecification(), const
<Symbol, dynamic>{});
On 2013/10/15 12:04:07, Lasse Reichstein Nielsen wrote:
> Can you replace the map with null, since it is never read?
> 
> You override ... 15 out of 22 methods. 
> Are you sure it wouldn't be easier to implement Zone and do the remaining
five,
> instead of passing irrelevant data to the super constructor.

Done.

[floitsch, 2013-10-15 13:32:19]

Committed patchset #2 manually as r28641 (presubmit successful).