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This is a reland of fd84ab8a.

This change:
1) Includes a new cipd package version that contains the 'size-classic'
   binary from the 10.15 SDK, missing in the original package
2) Can be coordinated with a re-land of the internal CL
   (https://chrome-internal-review.googlesource.com/c/chrome/src-internal/+/2404878)
   to keep the perf builders happy - they are stuck on the 10.14 SDK for
   reasons currently obscure.

Original change's description:
> mac: roll to 10.15 SDK
>
> This change rolls the hermetic Xcode to 11.2.1 aka 11B53, with the
> 10.15 SDK.
>
> Bug: 1023913
> Change-Id: I072a57b5f9c93bc08984b05d0de3ea62886a59dd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1964531
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
> Cr-Original-Commit-Position: refs/heads/master@{#725141}
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1993723
> Cr-Commit-Position: refs/heads/master@{#730238}

Bug: 1023913
Change-Id: I62d9e82673b2d3f4993fbd08654fed85c2319cfb
Tbr: thakis@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2022257Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#735493}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2024490
Cr-Commit-Position: refs/heads/master@{#735944}