Creating ErrorDialog from Throwable was already formatting error message
nicely because it is setting the css attribute 'whiteSpace' to 'pre'.
Creating ErrorDialog from an error message string was not setting this
css attribute resulting in line break being removed.
Fix this by making both use a private method to create error message
label. Also change the attribute from 'whiteSpace' to 'white-space'
which is the real name.
Change-Id: I5932c3d547b8ab232de2f866d0ad20d968804ee8
bf5cfebda8