[unified-heap] Fix ListenerLeakTest.* unit tests

The tests execute GC from JS which is not sufficient for unifiedh heap.
The fix adds proper GCs before asserting that the leak is not present.

Bug: 843903
Change-Id: Ieecf14acdbec96ebb6f612523ca0fa12aba92ad2
Reviewed-on: https://chromium-review.googlesource.com/c/1307395
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603892}
1 file changed