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/api/GroupElementHandle.java
* @throws SemanticException
	 *             if the property is not defined on this element
	 */
	abstract public void clearLocalProperties( ) throws SemanticException;
	/**
	 * Returns <code>true</code> if each of the given collection of element
	 * extends has a parent. Returns <code>false</code> otherwise. If the
	 * collection has no elements, also return <code>false</code>
	 * 
	 * @return <code>true</code> if each of the given collection of element
	 *         extends has a parent. Returns <code>false</code> otherwise. If
	 *         the collection has no elements, also return <code>false</code>
	 */
	abstract public boolean isExtendedElements( );
	/**
	 * This method returnt <code>true</code> in following condition:
	 * <p>
	 * 1. The multi selected elements are same type.
	 * <p>
	 * 2. And the multi selected elements have extends.
	 * <p>
	 * 3. If any of the given elements has local properties.
	 * <p>
	 * 
	 * @return <code>true</code> if the conditions is met.
	 */
	public final boolean hasLocalPropertiesForExtendedElements( )
	{
		if ( !isSameType( ) )
			return false;