We now have mousedown and dblclick event listeners on the root of the
        tree that forward the event to the node on the row the mouse is over.

        Reviewed by Tim Hatcher.

        * page/inspector/DocumentPanel.js:
        (WebInspector.DocumentPanel): Added a dblclick and mousedown event
        listeners to the root of the tree.
        (WebInspector.DocumentPanel._treeElementFromEvent): Added. Finds the
        tree element for the row underneath the mouse.
        (WebInspector.DocumentPanel._ondblclick): Added. Sends the dblclick
        event on to the tree element in the current row.
        (WebInspector.DocumentPanel._onmousedown): Added. Selects the tree
        element in the current row.
        * page/inspector/treeoutline.js:
        (TreeOutline.treeElementFromPoint): Added.
        (TreeElement.treeElementSelected): Changed to call
        TreeElement.isEventWithinDisclosureTriangle, and added an early return.
        (TreeElement.treeElementToggled): Ditto.
        (TreeElement.isEventWithinDisclosureTriangle): Added.
        * page/inspector/utilities.js:
        (Node.enclosingNodeOrSelfWithNodeNameInArray): Added.
        (Node.enclosingNodeOrSelfWithNodeName): Now just calls
        enclosingNodeOrSelfWithNodeNameInArray.
        (Elemnt.get totalOffsetLeft): Added.
        (Elemnt.get totalOffsetTop): Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31159 268f45cc-cd09-0410-ab3c-d52691b4dbfc