dart2js: Change how super tear-offs are registered.

dart2js: Change how super tear-offs are registered.

Previously, torn off super methods would be registered by emulating a
dynamic getter call using an exact TypeMask for the super class as the
receiver.

If the super class was abstract (or just not instantiated), using an
exact TypeMask is absurd since there are no objects with that exact
class.

Now, methods that have been registered as "needing super getter" are
always considered to have their getter invoked, removing the need to
emulate the dynamic getter call.

BUG=
R=johnniwinther@google.com

Committed: https://github.com/dart-lang/sdk/commit/a32a12f9000112414e7cf1b65e86e43dc2027d65

[asgerf, 2015-10-28 15:10:11]

asgerf@google.com changed reviewers:
+ johnniwinther@google.com

[Johnni Winther, 2015-10-28 16:46:00]

lgtm

[asgerf, 2015-11-06 10:49:11]

Committed patchset #4 (id:60001) manually as
a32a12f9000112414e7cf1b65e86e43dc2027d65 (presubmit successful).