Not possible to remove the 'li' element inside the table cell

Not possible to remove the 'li' element inside the table cell
https://bugs.webkit.org/show_bug.cgi?id=173148

Reviewed by Ryosuke Niwa.

Source/WebCore:

We need to add a new case for breaking out empty list items when they are
at the start of an editable area. Since list items can be also inside
table cells, we need to consider this kind of elements as well.

Tests: editing/deleting/delete-list-items-in-table-cell-1.html
       editing/deleting/delete-list-items-in-table-cell-2.html
       editing/deleting/delete-list-items-in-table-cell-3.html
       editing/deleting/delete-list-items-in-table-cell-4.html
       editing/deleting/delete-list-items-in-table-cell-5.html
       editing/deleting/delete-list-items-in-table-cell-6.html
       editing/deleting/delete-list-items-in-table-cell-7.html
       editing/deleting/delete-list-items-in-table-cell-8.html

* editing/TypingCommand.cpp:
(WebCore::TypingCommand::deleteKeyPressed):

LayoutTests:

Regression tests for different scenarios of list items removal.

* editing/deleting/delete-list-items-in-table-cell-1-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-1.html: Added.
* editing/deleting/delete-list-items-in-table-cell-2-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-2.html: Added.
* editing/deleting/delete-list-items-in-table-cell-3-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-3.html: Added.
* editing/deleting/delete-list-items-in-table-cell-4-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-4.html: Added.
* editing/deleting/delete-list-items-in-table-cell-5-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-5.html: Added.
* editing/deleting/delete-list-items-in-table-cell-6-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-6.html: Added.
* editing/deleting/delete-list-items-in-table-cell-7-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-7.html: Added.
* editing/deleting/delete-list-items-in-table-cell-8-expected.txt: Added.
* editing/deleting/delete-list-items-in-table-cell-8.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220398 268f45cc-cd09-0410-ab3c-d52691b4dbfc