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This is a reland after contacting the infra team about the addition of
dawn.googlesource.com to allowed_hosts. It also doesn't have the Dawn
build targets listed in BUILD.gn. These will be listed separately.

Dawn is a library implementing WebGPU in native. It uses SPIRV-Cross to
translate shaders from SPIRV to other shading languages, and requires
glfw for testing.

Adds the Zlib license to the list of allowed license for Android.

This also adds back shaderc that was very recently removed. So hopefully
a new third_party review isn't required.

BUG=chromium:870747

Change-Id: Ib5bb0530fc147e41a4f31796c30542e032bf0603
Reviewed-on: https://chromium-review.googlesource.com/c/1286135Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601445}