Fix Handler.Callback.handleMessage javadoc.

Currently arguments and return value annotations are applied to the
whole interface and aren't rendered at all:
https://developer.android.com/reference/android/os/Handler.Callback.html#handleMessage(android.os.Message)

Test: nothing to test.
Change-Id: I8cb44f7a6c339971b770e9bf769efee8294b4d28
Bug:36127602