Bug 150347 Support binary stream as preview image.
See 144843. We need model to save binary strame as report preview image. Currently, preview image is an external image. Maybe need a type to distinguish preview image type.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/parser/StructureState.java
*            the definition of the structure to create
	 * @return the structure instance created.
	 */
	static IStructure createStructure( StructureDefn structDefn )
	{
		synchronized ( StructureState.class )
		{
			if ( structDict == null )
				populateStructDict( );
		}
		assert structDefn != null;
		assert structDict != null;
		IStructure struct = null;
		try
		{
			Class c = (Class) structDict.get( structDefn.getName( )
					.toLowerCase( ) );
			assert c != null;
			struct = (IStructure) c.newInstance( );
		}
		catch ( InstantiationException e )
		{
			assert false;
		}
		catch ( IllegalAccessException e )
		{
			assert false;
		}
		return struct;
	}