The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4fb6e69738018eda7b9d387934d35188dd46da17

commit 4fb6e69738018eda7b9d387934d35188dd46da17
Author: skau <skau@chromium.org>
Date: Tue Jun 20 21:27:52 2017

Convert PpdCache and PpdProvider to TaskScheduler.

Part of the larger Chromium migration away from BrowserThreads.

BUG= 734279 ,  667892 

Review-Url: https://codereview.chromium.org/2939373003
Cr-Commit-Position: refs/heads/master@{#480963}

[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chrome/browser/chromeos/printing/ppd_provider_factory.cc
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_cache.cc
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_cache.h
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_cache_unittest.cc
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_provider.cc
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_provider.h
[modify] https://crrev.com/4fb6e69738018eda7b9d387934d35188dd46da17/chromeos/printing/ppd_provider_unittest.cc

Need to update the comment in PpdCache explaining why fetch and store can be performed on different sequences safely.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e85631c79cebfbf8c6004ac54eab93d9d00f4647

commit e85631c79cebfbf8c6004ac54eab93d9d00f4647
Author: skau <skau@chromium.org>
Date: Thu Jul 06 00:19:38 2017

Add sequencing comment to PpdCacheImpl.

We currently assume that any given file is only Stored once.  This
allows for Find and Store to run in different sequences at different
priorities.  Document this assumption in case this changes and a subtle
bug gets introduced.

BUG= 734279 

Review-Url: https://codereview.chromium.org/2958183002
Cr-Commit-Position: refs/heads/master@{#484401}

[modify] https://crrev.com/e85631c79cebfbf8c6004ac54eab93d9d00f4647/chromeos/printing/ppd_cache.cc