TestingProfile may destroy the profile directory while some background task still works with files inside of the directory. This leads to obscure flaky disk I/O errors in sqlite code:  https://crbug.com/839886 , https://crbug.com/839371.

Many tests use TestingProfile with the TestBrowserThreadBundle, for example, all subclasses of ChromeRenderViewHostTestHarness. After a test finishes, TestingProfile is destroyed on the UI thread together with the temporary profile directory, before all background tasks are executed. 

This CL adds artificial delays to show which tests may be affected by this error: https://crrev.com/c/1087055

See also this discussion thread:
https://groups.google.com/a/chromium.org/forum/?utm_medium=email&utm_source=footer#!topic/chromium-dev/-oH0n_O9Tjc