merge_pr_8401
A bug in a recent WIP CL caused multiple IPC messages to be sent with the same ID, but this was not caught by tests since tests only exercised messages serially. Fill that gap in our test coverage. Change-Id: I764fc7c41b1409fa6bf4a537ef2b64d7176afd3e Reviewed-on: https://chromium-review.googlesource.com/783520 Reviewed-by: Sasha Morrissey <[email protected]> Commit-Queue: Joshua Bell <[email protected]> Cr-Commit-Position: refs/heads/master@{#518479}