Use Runtime.gc instead of System.gc for DDMS.

System.gc doesn't always do a GC unless to attempt to run the
finalizers after you call System.gc.

Bug: 14325353
Change-Id: Iebed7fad5576d610cea13a86e7d3d46652c67478
Merge "Use Runtime.gc instead of System.gc for DDMS."
Merge remote-tracking branch 'aosp/master' into fml-master