This is necessary to build Windows ANGLE with the hermetic Win SDK.

BUG=angleproject:1569

Change-Id: Ic2c0aac6cab8d1a20f0bca8aea55418fe7defdc5
Reviewed-on: https://chromium-review.googlesource.com/734980Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>