Bug 249915 [Dialogs] TitleAreaDialog does not short circuit if message is null
M20080911-1700 When profiling use of a custom WizardDialog on Linux/GTK, a lot of time was spent in WizardPage.setMessage(...). It turns out that this was because we were setting a message of null after each keypress, and the page's description (DialogPage.getDescription()) was also null. In this case the short-circuit in TitleAreaDialog.setMessage(String, int) fails to notice that the message has not changed, and does a layout every time. For our dialog this takes about 40ms each time, which is noticeable when compounded with other work.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/TitleAreaDialog.java
if (message == null) 
				
				message = ""; 
			updateMessage(message);
			messageImageLabel.setImage(messageImage);
			setImageLabelVisible(messageImage != null);
		} else {
			
			
			String displayedErrorMessage = " " + errorMessage; 
			updateMessage(displayedErrorMessage);
			if (!showingError) {
				
				showingError = true;
				messageImageLabel.setImage(JFaceResources
						.getImage(DLG_IMG_TITLE_ERROR));
				setImageLabelVisible(true);
			}
		}
		layoutForNewMessage();
	}
	/**
	 * Re-layout the labels for the new message.
	 */
	private void layoutForNewMessage() {
		int verticalSpacing = convertVerticalDLUsToPixels(IDialogConstants.VERTICAL_SPACING);