tabindex rule throws error when it shouldn't

[corrieann]

Seems to be a recurrence of #1714

Snippet of HTML of the Element	<paper-input class="colab-replace-input" type="text" label="Replace with" tabindex="0" aria-disabled="false">
Impact	serious
Targets	.colab-replace-row > paper-input.colab-replace-input
FailureSummary	Fix any of the following: Element has a tabindex greater than 0
At least one check must have passed	CheckResult ID: tabindexImpact: seriousMessage: Element has a tabindex greater than 0

Can view the element in question on
https://colab.research.google.com by opening Edit -> Find and replace...
although if I do that and run axe via a Chrome extension, it's not triggering this error. It only seems to from axe-webdriver.

axe-core version: 2.5
axe-webdriver, extension or other integration version: 2.0

For Tooling issues:
- Platform:  Linux

[straker]

The bug is that paper-input redefines the tabIndex property of the element, so when we check for node.tabIndex <= 0, it returns undefined instead of a value. I'm not sure if this is a Polymer bug or something we have to start accounting for (custom elements overriding native properties of the HTMLElement).

[WilcoFiers]

Conclusion. This is a bug in paper-input, which does not allow accessing .tabIndex. That said, to avoid this type of issue, I do think we should drop using properties to get at attribute values. Using getAttribute() is more reliable, we've been burned by this before, so let's just solve it.

[straker]

Fix this problem, then work it in over time for the rest of the code base.

[padmavemulapati]

Not seeing the now, as we have done fix. Closing the ticket as issue not replicating