Replace explicit GetBlockingPool() flush with RunAllBlockingPoolTasksUntilIdle().

Adresses
content/public/test/download_test_observer.cc : GetBlockingPool()
entry of
https://docs.google.com/spreadsheets/d/18x9PGMlfgWcBr4fDz2SEEtIwTpSjcBFT2Puib47ZF1w/edit#gid=0

Bug: 667892
Change-Id: I74311b46bdf7e3ddda94bd868fbf4472b5a39609
Reviewed-on: https://chromium-review.googlesource.com/576372
Reviewed-by: PaweĊ‚ Hajdan Jr. <phajdan.jr@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487863}
1 file changed