Bug 23459 add preference option to turn off variable guessing on method completion
request from Adam
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/JavaEditorPreferencePage.java
initializeViewerColors(fPreviewViewer);
		
		String content= loadPreviewContentFromFile("ColorSettingPreviewCode.txt"); 
		IDocument document= new Document(content);
		IDocumentPartitioner partitioner= fJavaTextTools.createDocumentPartitioner();
		partitioner.connect(document);
		document.setDocumentPartitioner(partitioner);
		
		fPreviewViewer.setDocument(document);
		
		fOverlayStore.addPropertyChangeListener(new IPropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent event) {
				String p= event.getProperty();
				if (p.equals(AbstractTextEditor.PREFERENCE_COLOR_BACKGROUND) ||
					p.equals(AbstractTextEditor.PREFERENCE_COLOR_BACKGROUND_SYSTEM_DEFAULT))
				{
					initializeViewerColors(fPreviewViewer);
				}
				
				fPreviewViewer.invalidateTextPresentation();
			}
		});
		
		return fPreviewViewer.getControl();
	}
	
	/**
	 * Initializes the given viewer's colors.
	 * 
	 * @param viewer the viewer to be initialized