Convert deprecatedShadowAncestorNode() to shadowHost() in Editor.cpp
https://bugs.webkit.org/show_bug.cgi?id=108287

Reviewed by Hajime Morita.

This is the effort to convert deprecatedShadowAncestorNode() to shadowHost().

Since all the caller object of deprecatedShadowAncestorNode() is in a shadow tree, calling deprecatedShadowAncestorNode()
is equiavalent to calling shadowHost(). Also, for all the occurence of deprecatedShadowAncestorNode(), we don't need to
worry about nested ShadowDOM issues. So directly converting deprecatedShadowAncestorNode() to shadowHost() should be safe.

No new tests, simple refactoring.

* editing/Editor.cpp:
(WebCore::Editor::rangeOfString):
(WebCore::Editor::countMatchesForText):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141225 268f45cc-cd09-0410-ab3c-d52691b4dbfc