Use Guava's AbstractFuture to implement GceFuture.

This required adding Guava to the java Android.mk file, but allows
GceFuture to implement the more powerful ListenableFuture type with less
implementation.

AbstractFuture docs:
https://google.github.io/guava/releases/20.0/api/docs/com/google/common/util/concurrent/AbstractFuture.html

Bug: 110903523
Test: Ran cf_x86_64_phone-userdebug locally.
Change-Id: I305646473f3a0710f5315285912f4e106ed272c7
Merged-In: I305646473f3a0710f5315285912f4e106ed272c7
(cherry picked from commit 66032e13)