Bug 155943 "Restore Properties" is always enabled for extended chart
Steps to reproduce: 1.New a report, includes a library, extends lib.chart 2.Choose the chart Expected result: "Restore Properties" is disabled untill set/change any local properties for the chart Actual result: "Restore Properties" is always enabled
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/writer/ModuleWriter.java
protected void attribute( DesignElement obj, String attr, String propName )
	{
		ElementPropertyDefn prop = obj.getPropertyDefn( propName );
		assert prop != null;
		Object value = obj.getLocalProperty( getModule( ), prop );
		if ( value == null )
			return;
		String xml = prop.getXmlValue( getModule( ), value );
		if ( xml == null )
			return;
		writer.attribute( attr, xml );
	}
	/**
	 * Returns the tag according to the simple property type. If the property
	 * type is structure or structure list, this method can not be used.
	 * 
	 * <ul>
	 * <li>EXPRESSION_TAG, if the property is expression;
	 * <li>XML_PROPERTY_TAG, if the property is xml;
	 * <li>METHOD_TAG, if the property is method;
	 * <li>PROPERTY_TAG, if the property is string, number, and so on.
	 * </ul>
	 * 
	 * @param prop
	 *            the property definition
	 * @return the tag of this property
	 */
	protected String getTagByPropertyType( PropertyDefn prop )
	{
		assert prop != null;