Previously, we would blindly register new handler data, leading to us leaking
the old handler data. This meant we could then end up with overlapping handler
data where the instruction offset and landing pads didn't line up right.

Bug: v8:6841
Change-Id: Iedcd75925b8d9d59c8f9accf288cae954fdc568f
Reviewed-on: https://chromium-review.googlesource.com/677632
Commit-Queue: Eric Holk <eholk@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48144}