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This is a reland of f5345de1.
The problem with blink trybots was fixed: 
https://bugs.chromium.org/p/chromium/issues/detail?id=669240#c45

Original change's description:
> Bump macOS SDK to 10.12.
> 
> Bug: 669240
> Change-Id: I97cf582b97fac7aec2aa92bbdda02f5c17482c1d
> Reviewed-on: https://chromium-review.googlesource.com/570459
> Reviewed-by: Erik Chen <erikchen@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Erik Chen <erikchen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#491060}

Bug: 669240
Change-Id: I73b54eedbd0eab105adecfb6e817de8aa2b968ef
TBR: thakis@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/598670Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491499}