Previously a step-dependent reference was captured, which would not
exist anymore as soon as we change steps in async compilation. This fix
makes sure that we capture the pointer by copy, not by reference.

Change-Id: I7ff7e87b67b2fd379e6642d844a4c770cadf1f6c
Reviewed-on: https://chromium-review.googlesource.com/970964Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Kim-Anh Tran <kimanh@google.com>
Cr-Commit-Position: refs/heads/master@{#52079}