Called to run a dialog asking the user if they want to leave a page.
Return false (0) to use the default dialog implementation. Return true (1)
if the application will use a custom dialog or if the callback has been
executed immediately. Custom dialogs may be either modal or modeless. If a
custom dialog is used the application must execute |callback| once the
custom dialog is dismissed.
Called to run a dialog asking the user if they want to leave a page. Return false (0) to use the default dialog implementation. Return true (1) if the application will use a custom dialog or if the callback has been executed immediately. Custom dialogs may be either modal or modeless. If a custom dialog is used the application must execute |callback| once the custom dialog is dismissed.