- fix http://bugzilla.opendarwin.org/show_bug.cgi?id=8298
          REGRESSION: Crash occurs when attempting to drag selection into
          Depart/Return input fields at http://www.travelocity.com/
        - remove the mutation event listener that's installed all the time,
          since it slows things down a bit

        Calling SelectionController::nodeWillBeRemoved from Document::notifyBeforeNodeRemoval
        fixes the crash, which was happening because the call that was removing the text
        node, removeChildren, does not send a "node removed" mutation event (it sends a
        "subtree modified" mutation event instead). So this change alone fixes the crash.

        But I also changed setInnerText to not blow away the text node each time the value
        is changed, and that makes the test case behave even better -- you don't even lose
        the selection; it works as it did with the NSTextField-based text field.

        * manual-tests/input-empty-on-focus.html: Added.

        * page/Frame.h: Tweaked a few comments and functions related to selection.
        * page/Frame.cpp: (WebCore::Frame::dragCaret): Made non-const.

        * dom/Document.cpp: (WebCore::Document::notifyBeforeNodeRemoval):
        Call nodeWillBeRemoved on the two selection controllers before removing
        a node from the document.

        * editing/SelectionController.h: Tweak formatting. Remove MutationListener
        class and m_mutationListener field.
        * editing/SelectionController.cpp:
        (WebCore::SelectionController::SelectionController): Remove code to set up
        the mutation event listener.
        (WebCore::SelectionController::setSelection): Remove code to maintain the
        mutation event listener.

        * html/HTMLElement.cpp:
        (WebCore::HTMLElement::setInnerHTML): In cases where the container has only a
        single child use replaceChild, and in cases where the HTML being inserted
        also has only a single child and both are text nodes use setData. It's common
        to use setInnerHTML to set something that's just text.
        (WebCore::HTMLElement::setInnerText): Same as above, but simpler since the
        thing we're replacing with is always text.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@13889 268f45cc-cd09-0410-ab3c-d52691b4dbfc