The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4b451b9da21629300f09b82d291819c90a0b7fe0

commit 4b451b9da21629300f09b82d291819c90a0b7fe0
Author: Min Qin <qinmin@chromium.org>
Date: Fri Jun 16 20:20:12 2017

Fix a crash when saving a link to mhtml file

Saving a link to mhtml file will kick off an async task
However, before the async task completes, download could get canceled.
This will cause a crash in SavePackage::OnMHTMLGenerated()

BUG= 732874 

Change-Id: I1552b5f6e1e3121a5b1509dbc58327d71cc2d2fa
Reviewed-on: https://chromium-review.googlesource.com/533895
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#480148}
[modify] https://crrev.com/4b451b9da21629300f09b82d291819c90a0b7fe0/content/browser/download/save_package.cc
[modify] https://crrev.com/4b451b9da21629300f09b82d291819c90a0b7fe0/content/browser/download/save_package_browsertest.cc