Fix narrowing for null checks in type graph inferrer.

Fix narrowing for null checks in type graph inferrer.

BUG=
R=floitsch@google.com

Committed: https://code.google.com/p/dart/source/detail?r=39325

[floitsch, 2014-08-11 14:04:07]

LGTM.

[herhut, 2014-08-15 14:03:01]

This version makes sure to use the correct version of dynamic  for consistency.

[floitsch, 2014-08-15 17:37:44]

LGTM.

https://codereview.chromium.org/465433003/diff/20001/sdk/lib/_internal/compil...
File sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
(right):

https://codereview.chromium.org/465433003/diff/20001/sdk/lib/_internal/compil...
sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart:226:
? dynamicType.type.nonNullable()
Why is this necessary?
Isn't that the same?

[herhut, 2014-08-18 08:06:51]

https://codereview.chromium.org/465433003/diff/20001/sdk/lib/_internal/compil...
File sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart
(right):

https://codereview.chromium.org/465433003/diff/20001/sdk/lib/_internal/compil...
sdk/lib/_internal/compiler/implementation/inferrer/type_graph_inferrer.dart:226:
? dynamicType.type.nonNullable()
On 2014/08/15 17:37:44, floitsch wrote:
> Why is this necessary?
> Isn't that the same?

We can have [subclass object] and [subtype object], which contain the same set
of classes but we use the former for dynamic, whereas we would normally create
the latter for narrowing.
Unfortunately, we often use structural equality for type comparisons, where
subtype object != subclass object. In that sense, they are not the same.

[herhut, 2014-08-18 08:07:44]

Committed patchset #2 manually as 39325 (presubmit successful).