This patch is imported from https://bugs.webkit.org/show_bug.cgi?id=108675
written by Sukolsak Sakshuwong, sukolsak@gmail.com.

InsertHTML command renders inserting HTML fragment by paragraph element as child node of editing host for extracting inserted text by plainText(). This rendering is affected by inherited style and makes texts invisible.

This patch changes plainText() to ignore style visibility to avoid losing text.

BUG=248496
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/16801004

git-svn-id: svn://svn.chromium.org/blink/trunk@154374 bbb929c8-8fbe-4397-9dbb-9b2b20218538