Add utility process sandbox test for Linux.

This ensures that every utility process sandbox type actually results in
the created process being sandboxed. This has always been important, but
will become slightly more important when we start spawning from an
unsandboxed zygote.

This works by creating a SandboxStatusService mojo service which is test
only and exposes it on created utility processes. The test then simply
creates a utility process with every sandbox type ensures the sandbox
status is non-zero for types which should be sandboxed.

R=rsesek

Bug: 22703,1049234
Test: It's all tests!
Change-Id: I512f7aa77c20ba66e66cf448bfdabf5865a487e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2055993
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742861}

• content/browser/OWNERS[diff]
• content/browser/utility_process_sandbox_browsertest.cc[Added - diff]
• content/shell/BUILD.gn[diff]
• content/shell/utility/shell_content_utility_client.cc[diff]
• content/shell/utility/shell_content_utility_client.h[diff]
• content/test/BUILD.gn[diff]
• content/utility/soda/soda_sandbox_hook_linux.cc[diff]
• services/service_manager/sandbox/sandbox_type.h[diff]
• services/service_manager/tests/BUILD.gn[diff]
• services/service_manager/tests/sandbox_status.test-mojom[Added - diff]
• services/service_manager/tests/sandbox_status_service.cc[Added - diff]
• services/service_manager/tests/sandbox_status_service.h[Added - diff]