Bug 49182 What should canceling setRawClasspath do ?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/viewsupport/GoToBackProgressMonitorDialog.java
public void beginTask(final String name, final int totalWork) {
			if (fWrapped != null) {
				fWrapped.beginTask(name, totalWork);
			}
			if (fInBackground) {
				return;
			}
			if (progressIndicator.isDisposed())
				return;
			
			if (name == null)
				task= "";
			else	
				task= name;
			
			getShell().getDisplay().asyncExec(new Runnable() {
				public void run() {
					internalBeginTask(name, totalWork);	
				}
			});
		}
		
		private void internalBeginTask(String name, int totalWork) {
			if (progressIndicator.isDisposed())
				return;
			
			String s= task;
			if (s.length() <= 0)
				s= DEFAULT_TASKNAME;
			setDialogMessage(s);