Bug 208101 [Markers] Tasks content has mark completed enabled for non editable tasks
I20071030-0100 Mark completed is enabled for tasks that are not editable
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/provisional/views/markers/ExtendedMarkersView.java
MarkerGroup getCategoryGroup() {
		return builder.getCategoryGroup();
	}
	/**
	 * Return the clipboard for the receiver.
	 * 
	 * @return Clipboard
	 */
	Clipboard getClipboard() {
		if (clipboard == null)
			clipboard = new Clipboard(viewer.getControl().getDisplay());
		return clipboard;
	}
	/**
	 * Return the content provider for the receiver.
	 * 
	 * @return ITreeContentProvider
	 * 
	 */
	private ITreeContentProvider getContentProvider() {
		return new ITreeContentProvider() {
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.jface.viewers.IContentProvider#dispose()
			 */
			public void dispose() {
			}
			/*
			 * (non-Javadoc)