Make embedder.serviceRegistry return a ServiceRegistry instead of ServiceRegistryProxy.
Make embedder.serviceRegistry return a ServiceRegistry instead of ServiceRegistryProxy.

The proxy has methods like close() that I think we're not intending to expose to the
caller. The ServiceRegistry is just the interface itself. This also avoids users of
the API from having to add a .ptr to their usages of the registry.

BUG=
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1053883002

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