tree eff1232b61c2d9f43cba4bf4773a6de261a44b9e
parent d3a338c1d1faea3e27ff488a5eb76af5d3829692
author Narayan Kamath <narayan@google.com> 1460470688 +0100
committer Narayan Kamath <narayan@google.com> 1460542914 +0100

ConcurrentHashMap: update API for keySet.

On Android M and earlier, keySet() returned a Set<K>. Changing the
return type to a type that doesn't exist on previous releases is an
incompatible change. We therefore revert it so that applications that
compile against the Android N SDK will continue to work on older
releases.

Note that there is no API update that accompanies this change. Due to
an asymmetry in doclava, this method is absent from the *api.txt files
but *does* exist in the stubs.

bug: 28099367

(cherry picked from commit 0ee1606ffb8586014fb3ea6e540c07d7180d9e9e)

Change-Id: I912679f8606954640e1004c2ccf8afa0e31fa940