[Push] Enable PushManager.hasPermission() in browser tests.
Enables PushManager.hasPermission() as a transition until the Permissions API
can be used in order to get that information. It will save a lot of trouble in
changing the current test in order to no longer use hasPermission() then change
them again to use the Permissions API.
This is a three sided CL:
1- https://codereview.chromium.org/
926793004
2- <this>
3- https://codereview.chromium.org/
936873002
BUG=449178
Review URL: https://codereview.chromium.org/
937563004
Cr-Commit-Position: refs/heads/master@{#317512}