Define TAG in LoopbackExperiment

Previously LoopbackExperiment used the base class's TAG, but we've
defined one in LoopbackExperiment in favor of specificity.

In addition, this fixes errors created by proguard when building with
OpenJDK.

Change-Id: I6338f6499fbb4664988058e4f202b45d4fb80c1d
2 files changed