Fold leaks that are referenced by other leaks

Find leaks that have no references at all, or are only referenced by
other leaks in the same strongly connected component, and hide all
referenced leaks.

Bug: 27208635
Change-Id: Ifbfd14e24e2ba0f8af7c1b887e57f34362720f2d
(cherry picked from commit 8e8f34c5)