This makes jumbo_file_merge_limit=50 work again.

Bug: chromium:770684
Change-Id: I5db6566da876d71ea6ba50ff03b7652074b0a35f
Reviewed-on: https://chromium-review.googlesource.com/725818Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@vewd.com>
Cr-Commit-Position: refs/heads/master@{#48728}