Convert test to QuitClosure

Use a QuitClosure instead of RunUntilIdle in the CupsPrintersHandlerTest.
Test started failing if CupsPrinterManager creation was delayed.

Bug: 954623
Change-Id: I0ce986ce0995f678197b88c06186737ab56787aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579325
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653650}
1 file changed