Remove RunUntilIdle from WaitForResult.

Remove RunLoop::RunUntilIdle() from
TestCompletionCallbackBaseInternal::WaitForResult()
as suggested by a TODO.

Review-Url: https://codereview.chromium.org/2607123002
Cr-Commit-Position: refs/heads/master@{#441538}
13 files changed