This might be a duplicated of crbug.com/678481

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a086f601b68520d15e484aeff04efde78c9d596d

commit a086f601b68520d15e484aeff04efde78c9d596d
Author: tansell <tansell@chromium.org>
Date: Thu Jun 22 13:28:02 2017

LayoutTests: Disabling appcache-manifest-with-non-existing-file

The following layout test(s) is (failing|flaky) on Mac:

 * http/tests/inspector/appcache/appcache-manifest-with-non-existing-file.html
 * virtual/mojo-loading/http/tests/inspector/appcache/appcache-iframe-manifests.html

BUG= 735906 
TBR=dpranke@chromium.org,mcgreevy@chromium.org,qyearsley@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2947183003
Cr-Commit-Position: refs/heads/master@{#481516}

[modify] https://crrev.com/a086f601b68520d15e484aeff04efde78c9d596d/third_party/WebKit/LayoutTests/TestExpectations

Summary wrong?

Also, looks like the flakiness isn't particularly worse on these two than on other */http/tests/inspector/appcache/* tests.

WebKit Mac10.11 (dbg) crashes:

STDERR: [8385:1295:0622/082038.086253:1178802146699:FATAL:render_frame_devtools_agent_host.cc(793)] Check failed: !pending_.