tree cbe3cde703c343c12ea63387a92e8bfab9c4e384
parent 1c1f46429d5af06165045ceddb48f96072073699
author Jennifer Messerly <jmesserly@google.com> 1500510969 -0700
committer Jennifer Messerly <jmesserly@google.com> 1500510973 -0700

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

Review-Url: https://codereview.chromium.org//2978383002 .