Bug 312959 [Import/Export] importing file from big disk hangs UI
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/dialogs/ResourceTreeAndListGroup.java
treeViewer = new CheckboxTreeViewer(tree);
        treeViewer.setContentProvider(treeContentProvider);
        treeViewer.setLabelProvider(treeLabelProvider);
        treeViewer.addTreeListener(this);
        treeViewer.addCheckStateListener(this);
        treeViewer.addSelectionChangedListener(this);
    }
    /**
     * Returns a boolean indicating whether the passed tree element should be
     * at LEAST gray-checked.  Note that this method does not consider whether
     * it should be white-checked, so a specified tree item which should be
     * white-checked will result in a <code>true</code> answer from this method.
     * To determine whether a tree item should be white-checked use method
     * #determineShouldBeWhiteChecked(Object).
     *
     * @param treeElement java.lang.Object
     * @return boolean
     * @see #determineShouldBeWhiteChecked(Object)
     */
    protected boolean determineShouldBeAtLeastGrayChecked(Object treeElement) {
        
        
        List checked = (List) checkedStateStore.get(treeElement);
        if (checked != null && (!checked.isEmpty())) {
			return true;
		}
        
        
        if (expandedTreeNodes.contains(treeElement)) {
            Object[] children = treeContentProvider.getChildren(treeElement);