[unified-heap] Fix termination sequence for EmbedderHeapTracer

Garbage collection needs to be finalized before unsetting the
EmbedderHeapTracer pointer.

Otherwise, an already running GC may not be properly finalized and the
GC is left in a undefined state which the subsequent follow up GCs
discover.

Bug: 843903
Change-Id: I4dc73005174a1b99dfda96ef379fe62bf5b34dbe
Reviewed-on: https://chromium-review.googlesource.com/1243247
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594024}
1 file changed