Update build tools to newer gn.

Pasted from Chromium DEPS on 3/17/17.

R=reed@google.com

Change-Id: Ie1b93fadbad9e24b4a547f237df602a7257138f7
Reviewed-on: https://skia-review.googlesource.com/9831
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Reed <reed@google.com>
1 file changed