[LFC] Implement width computation for non-replaced out of flow elements.

[LFC] Implement width computation for non-replaced out of flow elements.
https://bugs.webkit.org/show_bug.cgi?id=185598

Reviewed by Antti Koivisto.

* layout/FormattingContext.cpp:
(WebCore::Layout::FormattingContext::computeWidth const):
(WebCore::Layout::FormattingContext::computeOutOfFlowWidth const):
(WebCore::Layout::FormattingContext::layoutOutOfFlowDescendants const):
(WebCore::Layout::FormattingContext::computeOutOfFlowNonReplacedWidth const):
(WebCore::Layout::FormattingContext::shrinkToFitWidth const):
* layout/FormattingContext.h:
* layout/blockformatting/BlockFormattingContext.cpp:
(WebCore::Layout::BlockFormattingContext::layout const):
* layout/displaytree/DisplayBox.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@231756 268f45cc-cd09-0410-ab3c-d52691b4dbfc