Propagate --use-mock-keychain switch to utility process

On Mac, the --use-mock-keychain is needed by the network service to
load the correct keychain.

Bug: 960926
Change-Id: Icae42bc00198e6178de923b23598101248e1add1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627937
Commit-Queue: John Chen <johnchen@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662844}
3 files changed