This test looks flaky.

Sample output from:
https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.mac%2FMac10.9_Tests__dbg_%2F48222%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests%2F0%2Flogs%2FPrintPreviewUIBrowserTest.InvalidSettingsError%2F0

[15956:771:1217/141459.943620:INFO:CONSOLE(1225)] "Running TestCase PrintPreviewUIBrowserTest.InvalidSettingsError", source: test_api.js (1225)
[15956:771:1217/141501.322790:ERROR:CONSOLE(14565)] "Uncaught TypeError: Cannot read property 'classList' of null", source: chrome://print/print_preview.js (14565)
[15956:771:1217/141502.321288:ERROR:web_ui_browser_test.cc(475)] CONDITION FAILURE: encountered javascript console error(s):
[15956:771:1217/141502.321335:ERROR:web_ui_browser_test.cc(477)] JS ERROR: '[15956:771:1217/141501.322790:ERROR:CONSOLE(14565)] "Uncaught TypeError: Cannot read property 'classList' of null", source: chrome://print/print_preview.js (14565)
'
[15956:771:1217/141502.321356:ERROR:web_ui_browser_test.cc(479)] JS call assumed failed, because JS console error(s) found.
gen/chrome/test/data/webui/print_preview/print_preview_ui_browsertest-gen.cc:1232: Failure
Value of: RunJavascriptTestF( true, "PrintPreviewUIBrowserTest", "InvalidSettingsError")
  Actual: false
Expected: true

Disabling the test...
https://chromium-review.googlesource.com/c/830993/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b459327f1581343c8ca47539150370539ed4f164

commit b459327f1581343c8ca47539150370539ed4f164
Author: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Mon Dec 18 03:25:36 2017

Disable PrintPreviewUIBrowserTest.InvalidSettingsError because of test flakiness

Bug:  795626 
Change-Id: If0016e86ca495cee54bf4b7a845f5adda8e6b65b
TBR: dpapad@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/830993
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524647}
[modify] https://crrev.com/b459327f1581343c8ca47539150370539ed4f164/chrome/test/data/webui/print_preview/print_preview_ui_browsertest.js

@nhiroki: Given that this test was only flaking on Mac, should it have been disabled for Mac only? It seems it was disabled entirely.

@rbpotter: Looking at the error
"Uncaught TypeError: Cannot read property 'classList' of null", source: chrome://print/print_preview.js (14565)

It seems that in some cases the line at [1] executes either before decorateInternal(), or after exitDocument(). Maybe a race condition in the test?

[1] https://cs.chromium.org/chromium/src/chrome/browser/resources/print_preview/previewarea/preview_area.js?l=438

Reg c#4: Sorry, I didn't know C/C++ marco is available in the JS file.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e28af6a1633a2abc7e0d937d5bfc65c1032ce4e6

commit e28af6a1633a2abc7e0d937d5bfc65c1032ce4e6
Author: rbpotter <rbpotter@chromium.org>
Date: Wed Dec 20 18:49:49 2017

Print Preview: Fix tests

Tests were failing due to setTimeout() in preview area expiring after
dialog was closed. Cancel the timeout in exitDocument() to prevent this
and re-enable tests.

Bug:  795626 ,  795658 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ie569c9509b459dadcf3c6aefba7de7624ca363de
Reviewed-on: https://chromium-review.googlesource.com/833496
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525386}
[modify] https://crrev.com/e28af6a1633a2abc7e0d937d5bfc65c1032ce4e6/chrome/browser/resources/print_preview/previewarea/preview_area.js
[modify] https://crrev.com/e28af6a1633a2abc7e0d937d5bfc65c1032ce4e6/chrome/test/data/webui/print_preview/print_preview_ui_browsertest.js