It looks like the test creates a "/test" directory and cleans it up after use but not before use. If any other test creates a similar entry and doesn't clean it up it could be getting confused. Will need to inspect the output to know for sure

From: 

https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Mac_-_RandomOrder/29/layout-test-results/fast/filesystem/cross-filesystem-op-pretty-diff.html

Failure is:

ERROR:dest: createDirectory(/test): TypeMismatchError

So yeah, hypothesis seems correct.

Tools/Scripts/run-webkit-tests --child-processes=1 --order=random --seed=1480444199 fast/filesystem/cross-filesystem-op.html fast/filesystem/null-arguments.html 

Several of the tests leave behind cruft like '/test' files. I don't want to muck with the tests too much but I'll make some additional fixes where easy.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5

commit 7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5
Author: jsbell <jsbell@chromium.org>
Date: Wed Nov 30 02:05:47 2016

Make fast/filesystem/cross-filesystem-op.html insensitive to test order

Test assumed that '/test' could be created as a directory, which
would fail if a previous test left '/test' behind as a file (as some do).
Make the test clear out the root first, as many other tests do.

Also tweak a few other tests to clean up when done, but not all tests
were inspected/updated.

R=jeffcarp@chromium.org
BUG= 663852 

Review-Url: https://codereview.chromium.org/2537193003
Cr-Commit-Position: refs/heads/master@{#435125}

[modify] https://crrev.com/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5/third_party/WebKit/LayoutTests/RandomOrderExpectations
[modify] https://crrev.com/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5/third_party/WebKit/LayoutTests/fast/filesystem/cross-filesystem-op.html
[modify] https://crrev.com/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5/third_party/WebKit/LayoutTests/fast/filesystem/not-enough-arguments.html
[modify] https://crrev.com/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5/third_party/WebKit/LayoutTests/fast/filesystem/null-arguments.html
[modify] https://crrev.com/7727a1c513f1cd6658e05e2fe95ccf293b5cc8d5/third_party/WebKit/LayoutTests/fast/filesystem/resources/null-arguments-worker.js

Looking good on the bots so far.