fix MapKeySet.lookup to be a valid override in strong mode

fix MapKeySet.lookup to be a valid override in strong mode

This was uncovered when fixing interface checking (https://github.com/dart-lang/sdk/issues/29766, https://github.com/dart-lang/sdk/issues/29782)

R=matanl@google.com

Committed: https://github.com/dart-lang/collection/commit/a15382f5c5b1dbf5c1e338b727dbc78755caed0c

[Jennifer Messerly, 2017-07-19 23:47:36]

jmesserly@google.com changed reviewers:
+ lrn@google.com, matanl@google.com

[Jennifer Messerly, 2017-07-19 23:47:37]

https://codereview.chromium.org/2978383002/diff/1/lib/src/wrappers.dart
File lib/src/wrappers.dart (right):

https://codereview.chromium.org/2978383002/diff/1/lib/src/wrappers.dart#newco...
lib/src/wrappers.dart:452: E lookup(Object element) =>
after this change, this is now a valid implementation of Set.lookup:
https://api.dartlang.org/stable/1.24.2/dart-core/Set/lookup.html

[matanl, 2017-07-20 00:02:18]

lgtm

[Jennifer Messerly, 2017-07-20 00:36:17]

Description was changed from

==========
fix MapKeySet.lookup to be a valid override in strong mode

This was uncovered when fixing interface checking
(https://github.com/dart-lang/sdk/issues/29766,
https://github.com/dart-lang/sdk/issues/29782)
==========

to

==========
fix MapKeySet.lookup to be a valid override in strong mode

This was uncovered when fixing interface checking
(https://github.com/dart-lang/sdk/issues/29766,
https://github.com/dart-lang/sdk/issues/29782)

R=matanl@google.com

Committed:
https://github.com/dart-lang/collection/commit/a15382f5c5b1dbf5c1e338b727dbc7...
==========

[Jennifer Messerly, 2017-07-20 00:36:19]

Committed patchset #1 (id:1) manually as
a15382f5c5b1dbf5c1e338b727dbc78755caed0c (presubmit successful).