Bug 93400 LTK UI should provide official API for structural content in the preview page
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/internal/ui/refactoring/PreviewWizardPage.java
* to create their own custom tree content provider.
	 *
	 * @return the tree content provider used to fill the tree of changes
	 */
	protected ITreeContentProvider createTreeContentProvider() {
		return new ChangeElementContentProvider();
	}
	
	/**
	 * Creates the label provider used to render the tree of changes. Subclasses may override
	 * to create their own custom label provider.
	 *
	 * @return the label provider used to render the tree of changes
	 */
	protected ILabelProvider createTreeLabelProvider() {
		
		return new ChangeElementLabelProvider();
	}
	
	/* (non-JavaDoc)
	 * Method defined in RefactoringWizardPage
	 */
	protected boolean performFinish() {
		UIPerformChangeOperation operation= new UIPerformChangeOperation(getShell().getDisplay(), fChange, getContainer());
		FinishResult result= getRefactoringWizard().internalPerformFinish(InternalAPI.INSTANCE, operation);
		if (result.isException())
			return true;
		if (result.isInterrupted())
			return false;
		RefactoringStatus fValidationStatus= operation.getValidationStatus();