Add System.runFinalization() call

Lone calls to System.gc() generally don't do anything.
Runtime.getRuntime().gc() would force a GC, but it would be ineffective
without waiting for reference processing and finalization to complete.
Adding the runFinalization() call implicitly makes the preceding GC call
effective.

Bug: 183912710
Test: Treehugger
Change-Id: I0f4806b8e3f9ca898eb7ea1b1c8de14aa94e2646