The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b3fcf2065c6e6e7617462a050e6503a844caaa9b

commit b3fcf2065c6e6e7617462a050e6503a844caaa9b
Author: Xing Liu <xingliu@chromium.org>
Date: Tue Sep 12 00:52:08 2017

Fix a flaky browser test for parallel download.

ParallelDownloadResumption is flaky previously, the cause is an edge
case bug in download resumption with a prallel download, that first
hole can be filled before creating parallel requests.

The impact of this bug is very small. Repro rate in browser test is
only 1-2%, and resumption only happens for 4.9% for all downloads.

Bug:  762763 
Change-Id: I00efbc14ec40f484f3ef111f8237894c4009ba6d
Reviewed-on: https://chromium-review.googlesource.com/653314
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501127}
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/download_browsertest.cc
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/mock_download_item_impl.cc
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/mock_download_item_impl.h
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/parallel_download_job.cc
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/parallel_download_job.h
[modify] https://crrev.com/b3fcf2065c6e6e7617462a050e6503a844caaa9b/content/browser/download/parallel_download_job_unittest.cc