Bug 199834 Enable access to IContent object in IReportItemPresentation layer
In IReportItemPresentation layer, the extended item may want to access properties from current IContent object, for example, bookmark, content style. So we need expose the content object in this layer.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/extension/IReportItemGeneration.java
* serializes the extended item generation time state. The application
	 * developer should not assume that the output stream is a file stream.
	 * Presentation engine guarantees that a corresponding input stream is
	 * available for deserializing what is written by this function.
	 * 
	 * @param ostream
	 *            the output stream to write the generation time state of the
	 *            extended item to
	 * @throws BirtException
	 *             when there is a problem serializing the extended item state
	 */
	public abstract void serialize( OutputStream ostream ) throws BirtException;
	/**
	 * Get the size of the extended item. The size is a Dimension object. The
	 * width and height can only be in absolute units (inch, mm, etc.) or pixel.
	 * It can not be a relative size such as 150% or 1.2em. Notice that an
	 * extended item can obtain its design-time size information by querying DE.
	 * This function is needed because the actual size may not be the same as
	 * the design-time size.
	 * 
	 * @return the size of the extended item. Return null if the size does not
	 *         matter or can not be determined.
	 */
	public Size getSize( );
	/**
	 * Performs clean up work
	 */
	public void finish( );
}