Remove toplevel inference restriction hints, and restore as much

Remove toplevel inference restriction hints, and restore as much
toplevel inference as possible to match the new front end toplevel
inference.

BUG=
R=scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/c595972d746b750dea0c56c9ed767afb961f0d09

[Leaf, 2017-07-21 19:50:23]

leafp@google.com changed reviewers:
+ paulberry@google.com, scheglov@google.com

[Leaf, 2017-07-21 19:50:24]

This is my attempt to restore as much of the previous status quo as possible to
bring the current analyzer closer to being in line with the planned front end
behavior.  

I poked at a lot of code that I don't understand very well, so Paul or
Konstantin, one of you should probably look at the changes in link.dart with a
fairly sharp eye.

I can get rid of some of the hint codes in codes.dart if desired, I just worried
that it would be a breaking change and should perhaps be postponed.

[scheglov, 2017-07-23 23:09:15]

LGTM

[Leaf, 2017-07-25 22:57:16]

Description was changed from

==========
Remove toplevel inference restriction hints, and restore as much
toplevel inference as possible to match the new front end toplevel
inference.

BUG=
==========

to

==========
Remove toplevel inference restriction hints, and restore as much
toplevel inference as possible to match the new front end toplevel
inference.

BUG=
R=scheglov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/c595972d746b750dea0c56c9ed767afb961f0d09
==========

[Leaf, 2017-07-25 22:57:18]

Committed patchset #4 (id:60001) manually as
c595972d746b750dea0c56c9ed767afb961f0d09 (presubmit successful).