Able to repro. Output locally and on the bots is just a spurious extra (or sometimes missing):

CONSOLE WARNING: line 22: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.

I see that when running w/o random order, so it appears to just be general flakiness. http/tests/appcache/obsolete-error-events.html on the dashboard shows as generally flaky anyway.

Many of the appcache tests use a trick where the manifest is a PHP file which can be accessed with ?command=XXX to control server behavior (e.g. "connect" or "disconnect" to simulate online/offline behavior).

These 4 in particular have code like:

// If the manifest script happened to be in a wrong state, reset it.
var timeoutId = setTimeout(resetManifest, 100);

(where resetManifest does a sync XHR)

... which explains the random order flakiness: if a previous run left the server in a bad state, the test needs to do an extra XHR to reset it, causing the extra logging.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8

commit 1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8
Author: jsbell <jsbell@chromium.org>
Date: Wed Nov 30 22:31:15 2016

Deflake tests in http/tests/appcache/ when run in random order

The tests use sync XHR to poke the server to tweak the AppCache manifest
state. Since the manifest is PHP server is re-used across tests the
initial state could be unexpected. The tests handled this as necessary,
but meant that a variable number of sync XHRs would be issued. Since
sync XHRs log a deprecation warning the output was flaky. Fix this
by switching server control to async XHR.

Additionally, obsolete-error-events.html would time out if no update
was needed, so handle the 'noupdate' event too.

BUG= 663860 
R=jeffcarp@chromium.org

Review-Url: https://codereview.chromium.org/2540833002
Cr-Commit-Position: refs/heads/master@{#435450}

[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/RandomOrderExpectations
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/main-resource-redirect-expected.txt
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/main-resource-redirect.html
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/non-html-expected.txt
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/non-html.xhtml
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/obsolete-error-events-expected.txt
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/obsolete-error-events.html
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/remove-cache-expected.txt
[modify] https://crrev.com/1b6aabf1422f519dfe93fde0ba65b04c3a7a60a8/third_party/WebKit/LayoutTests/http/tests/appcache/remove-cache.html