vpn-manager: explicitly specify base::StringPrintf

chromeos/process.h leaks a 'using base::StringPrintf' statement, which
will be removed. This CL updates vpn-manager code to explicitly specify
base::StringPrintf.

BUG=None
TEST=`FEATURES=test emerge-$BOARD platform2`

Change-Id: I83513e467fc6ea1665ff55279623b434b0d3af85
Reviewed-on: https://chromium-review.googlesource.com/196708
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
3 files changed