Android O MR1 SDK.

This updates:
 - build-tools to 27.0.1
 - platforms to 27
 - tools to 26.1.1

TBR=agrieve@chromium.org
Bug: 782848
Change-Id: I55c5facdd3f85024af93d62965596566aa9a40a6
Reviewed-on: https://chromium-review.googlesource.com/784090
Reviewed-by: John Budorick <jbudorick@chromium.org>