[jumbo] Unduplicate duplicated IsShuttingDown

Quick fix to unbreak jumbo builds. In
https://chromium-review.googlesource.com/c/chromium/src/+/1205976
a copy of IsShuttingDown was added and this patch changes the code
to instead use the original version.

TBR=kinuko@chromium.org,nhiroki@chromium.org

Bug: 715632
Change-Id: I2451fcaa009ec6403827cdb05cd3b47112c4681b
Reviewed-on: https://chromium-review.googlesource.com/1209703
Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#589148}
3 files changed