Bug 336225 Trim bars do not get unrendered by the rendering engine when trimmed window is unrendered
The trim bars are "ignored" by the rendering engine as it does not perform an unrendering pass on them when the parent trimmed window is being unrendered.
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
ServiceReference ref = context
					.getServiceReference(IThemeManager.class.getName());
			IThemeManager mgr = (IThemeManager) context.getService(ref);
			final IThemeEngine engine = mgr.getEngineForDisplay(display);
			
			IContributionFactory contribution = (IContributionFactory) appContext
					.get(IContributionFactory.class.getName());
			IEclipseContext cssContext = EclipseContextFactory.create();
			cssContext.set(IContributionFactory.class.getName(), contribution);
			display.setData("org.eclipse.e4.ui.css.context", cssContext); 
			
			if (cssResourcesURI != null) {
				
				engine.registerResourceLocator(new OSGiResourceLocator(
						cssResourcesURI));
			}
			engine.restore(cssTheme);
			
			appContext.set(IThemeEngine.class.getName(), engine);
			appContext.set(IStylingEngine.SERVICE_NAME, new IStylingEngine() {
				public void setClassname(Object widget, String classname) {
					((Widget) widget).setData(
							"org.eclipse.e4.ui.css.CssClassName", classname); 
					engine.applyStyles((Widget) widget, true);
				}
				public void setId(Object widget, String id) {
					((Widget) widget).setData("org.eclipse.e4.ui.css.id", id); 
					engine.applyStyles((Widget) widget, true);
				}
				public void style(Object widget) {