Removed the static field and made it an instance field on the
BundleBuilder.

Change-Id: I58a9f4a744654b262a3e47e6873baffb537eb21b
Reviewed-on: https://chromium-review.googlesource.com/c/1404444Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58709}