Print notice to stderr to avoid interfering with scripts that parse stdout.

Bug: 832386
Change-Id: Ifbcc52809213311489f5c8434b3c16ea53373e57
Reviewed-on: https://chromium-review.googlesource.com/1145697Reviewed-by: Michael Moss <mmoss@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>