Punting to rockot :)

Confirmed that this doesn't work.

I've looked into it more and it's because CreateFileMapping (https://cs.chromium.org/chromium/src/base/memory/shared_memory_win.cc?rcl=0&l=108) fails within a sandbox. We use named objects, and named objects apparently can't be created from within a sandbox.

The fix here is to broker shared buffer creation synchronously as we do on other platforms.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b214d02f960a60409d5163ef06e4d91ceb71e983

commit b214d02f960a60409d5163ef06e4d91ceb71e983
Author: rockot <rockot@chromium.org>
Date: Wed Sep 14 21:28:45 2016

Adds sync brokering to Windows EDK

We use a sync channel on other platforms to facilitate synchronous
shared buffer creation from within a sandbox. We need to do this
on Windows too.

This implements that, and adds a test for sandboxed shared buffer
creation.

BUG= 594883 

Review-Url: https://codereview.chromium.org/2264543003
Cr-Commit-Position: refs/heads/master@{#418679}

[add] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/browser/mojo_sandbox_browsertest.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/browser/service_worker/service_worker_version_unittest.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/public/test/OWNERS
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/public/test/test_mojo_app.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/public/test/test_mojo_app.h
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/public/test/test_mojo_service.mojom
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/shell/renderer/shell_content_renderer_client.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/shell/utility/shell_content_utility_client.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/content/test/BUILD.gn
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/embedder/platform_shared_buffer.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/BUILD.gn
[rename] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/broker_host.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/broker_host.h
[add] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/broker_win.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/node_controller.cc
[modify] https://crrev.com/b214d02f960a60409d5163ef06e4d91ceb71e983/mojo/edk/system/node_controller.h