Reviewed by Pavel Feldman.

        Web Inspector: Bugs in some corner cases in the text editor
        https://bugs.webkit.org/show_bug.cgi?id=58025

        This solves the following bugs:
        1) The very last _empty_ line would not be deleted if you hit a Backspace on it, or the selection text to be deleted is extended to the very bottom of the editor.
        2) An odd corner case: delete all source code from the editor, hit backspace on the only empty line, then add a character. In this case the browser will insert a TEXT node instead of a DIV node for a lineRow.

        * inspector/front-end/TextViewer.js:
        (WebInspector.TextEditorMainPanel.prototype._selectionToPosition):
        (WebInspector.TextEditorMainPanel.prototype._enclosingLineRowOrSelf):
        (WebInspector.TextEditorMainPanel.prototype._handleDOMUpdates):
        (WebInspector.TextEditorMainPanel.prototype._applyDomUpdates):
        (WebInspector.TextEditorMainPanel.prototype._collectLinesFromDiv):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@83285 268f45cc-cd09-0410-ab3c-d52691b4dbfc