CheckedFuture is deprecated in Guava 22.
Remove imports of CheckedFuture and refer to it with explicit
package name in the code, so we can suppress warnings where it's
used rather than suppressing for the whole class. The latter would
also suppress warnings if something else gets deprecated in future
and cause us to miss it.
Change-Id: I99d5021da205c9f1f4c6393ae3eb4c3e701efe20
(cherry picked from commit 58087a18a0a96ef58d6b0fe742799281cc50c9b0)
fe9e775fe5