Revert of Content in disabled input field should not be selectable. (patchset #4 id:80001 of https://codereview.chromium.org/2145323002/ )

Reason for revert:
It caused regression:
https://bugs.chromium.org/p/chromium/issues/detail?id=656736

Original issue's description:
> Content in disabled input field should not be selectable.
>
> Spec: https://html.spec.whatwg.org/multipage/forms.html#the-readonly-attribute:attr-input-readonly
>
> BUG=626581
>
> Committed: https://crrev.com/21d670d3e740b26dcdf63631d163c45a57d9531c
> Cr-Commit-Position: refs/heads/master@{#405717}

TBR=tkent@chromium.org,ramya.v@samsung.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=626581

Review-Url: https://codereview.chromium.org/2455853002
Cr-Commit-Position: refs/heads/master@{#428261}
6 files changed