In branch elimination phase, control paths are updated when visiting
the nodes. We first create a control path and then check if it is
same as the exisiting one. If it is the same we discard the newly
created one. Since these are created in the zone memory the memory
will not be released till the entire pass is over. This cl changes
it to first check if the control path has changed and create a new
path only if it has changed.

Bug: chromium:725664,v8:6150
Change-Id: I67fbea13036f85999c7ed366c571f8dc1c17a023
Reviewed-on: https://chromium-review.googlesource.com/563406Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46598}