Make PrinterConfigurer use OnceCallback.

The call site (LocalPrinterHandlerChromeos) relies on this callback to never be rerun anyway.
Now we assure this in compile time.

Bug: 625126
Change-Id: I81767ab1212184da898c51d05664fb2cff77ffbb
Reviewed-on: https://chromium-review.googlesource.com/721700
Commit-Queue: Vladislav Kuzkokov <vkuzkokov@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511521}
11 files changed