Cloning and linebox issues in multi-column layout.

Cloning and linebox issues in multi-column layout.
https://bugs.webkit.org/show_bug.cgi?id=78273

Reviewed by Eric Seidel.

Source/WebCore:

Tests: fast/multicol/span/clone-flexbox.html
       fast/multicol/span/clone-summary.html
       fast/multicol/span/textbox-not-removed-crash.html

* rendering/RenderBlock.cpp:
(WebCore::RenderBlock::clone): Fix cloning algorithm to take
care of cloning descendant classes of RenderBlock.
(WebCore::RenderBlock::splitBlocks): When we move our inline children
to cloneBlock, we need to clear our entire line box tree. Any descendant
child in the hierarchy could be a part of our line box tree and will
never get cleared since the child has moved to new parent cloneBlock.

LayoutTests:

* fast/multicol/span/clone-flexbox-expected.png:
* fast/multicol/span/clone-flexbox-expected.txt: Added.
* fast/multicol/span/clone-flexbox.html: Added. Test passes if we
see two RenderFlexibox in the rendertree.
* fast/multicol/span/clone-summary-expected.png: Added.
* fast/multicol/span/clone-summary-expected.txt: Added.
* fast/multicol/span/clone-summary.html: Added. Test passes if we
see two RenderSummary in the rendertree.
* fast/multicol/span/textbox-not-removed-crash-expected.txt: Added.
* fast/multicol/span/textbox-not-removed-crash.html: Added. Test
passes it we do not crash on m_hasBadParent assert in InlineBox.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108543 268f45cc-cd09-0410-ab3c-d52691b4dbfc