Add convenience retrace script for R8.

Test: R8_THROW_EXCEPTION_FOR_TESTING_RETRACE=1 \
      java -cp r8-master.jar com.android.tools.r8.R8 --help 2>&1 \
      | ./retrace-r8-master.sh

Change-Id: Iee18f25fcd1167bb7d557207d805757d1d023e6c
5 files changed