This is a first step towards support for opening more than one
turbolizer json file at once.

Change-Id: Id51ce47c59492ba63de03eceb0163fa1701ea500
Notry: true
Bug: v8:7327
Reviewed-on: https://chromium-review.googlesource.com/c/1407057
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58790}