Remove open generics Operation<? super T, U> from stream.compose().

Authored by markwei on Wed, Apr 12, 4:15 PM.

Description

Remove open generics Operation<? super T, U> from stream.compose().

Summary:
Instead, use Operation<T, U> and count on the fact that operators return an Operation<T extends WantedType> rather than Operation<WantedType>.

This is an attempt to fix travis ci build breakage https://travis-ci.org/material-motion/material-motion-android/builds/221482610

Reviewers: O2 Material Motion, O6 Material Android platform reviewers, Material Motion, featherless

Reviewed By: O2 Material Motion, Material Motion, featherless

Tags: Material Motion

Differential Revision: http://codereview.cc/D3037