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/writer/DesignWriter.java
* <p>
 * Because the XML schema was designed for to be understood by humans, the
 * schema is not a literal representation of the model. Instead, properties are
 * named and grouped in a way that is easiest to explain and understand. This
 * means that the writer has to do a bit more work to write the design, the the
 * extra work here is well worth the savings to the many customers who will read
 * the design format.
 * 
 */
public class DesignWriter extends ModuleWriter
{
	/**
	 * The design context used to convert units.
	 */
	private ReportDesign design;
	/**
	 * Constructs a writer with the specified design.
	 * 
	 * @param design
	 *            the internal representation of the design
	 */
	public DesignWriter( ReportDesign design )
	{
		this.design = design;
	}
	/**
	 * Write the top-level Report tag, and the properties and contents of the
	 * report itself.
	 * 
	 * @param obj