This fixes a corner case of rewriting the transition trees, where the
"interesting symbols" bit was not properly forwarded.

Drive-by-fix: Introduce additional checking in Map::ConnectTransition to
make it easier for clusterfuzz to detect cases we might have missed.

R=mstarzinger@chromium.org

Bug: chromium:751109
Change-Id: I3f1a1e6232db9b3694064b3d4e9f37255b018acc
Reviewed-on: https://chromium-review.googlesource.com/597669Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47075}