Ignore <input> and <textarea>'s user-select styling

The CSS spec says that user-select does "selective inheritance",
see https://drafts.csswg.org/css-ui-4/#propdef-user-select.

<input> and <textarea> are two elements that are affected
by this. These elements should not inherit user-select from
parent elements.

Fixed problem:
<input|textarea readonly|disabled> could inherit
"user-select: none".

This regressed because
removed input|textarea's default user-select styling.

Make all text controls always selectable. This is done in

Interoperability note:
<input readonly style="user-select: none"
value="Chrome 61 cannot select this.">. This CL fixes
this by ensuring that all text fields (i.e also readonly fields)
are always selectable (no matter user-select styling).

In other words, <input> and <input readonly> now behave in
the same way (both always allow selections) which aligns
us with Firefox and Edge.

BUG=761433, 764316

(cherry picked from commit ba7c210328c00a6693ddc5da6504f8520bb3bdc2)

Change-Id: I89fc94a2a04caf3a87b12a9071081dafd48a8727
Reviewed-on: https://chromium-review.googlesource.com/663217
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Hugo Holgersson <hugoh@opera.com>
Cr-Original-Commit-Position: refs/heads/master@{#503793}
Reviewed-on: https://chromium-review.googlesource.com/685655
Reviewed-by: Hugo Holgersson <hugoh@opera.com>
Cr-Commit-Position: refs/branch-heads/3202@{#453}
Cr-Branched-From: fa6a5d87adff761bc16afc5498c3f5944c1daa68-refs/heads/master@{#499098}
2 files changed