From http://codecorner.galanter.net/2014/09/02/reenable-showmodaldialog-in-chrome/
It's deprecated by design. You can re-enable showModalDialog support, but only temporarily – until May of 2015. Use this time to create alternative solutions.
Here’s how to do it in Chrome for Windows. Open Registry Editor (regedit) and create following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome\EnableDeprecatedWebPlatformFeatures
Under the EnableDeprecatedWebPlatformFeatures
key create a string value with name 1
and value of ShowModalDialog_EffectiveUntil20150430
. To verify that the policy is enabled, visit chrome://policy URL.
gpedit.msc
or using these utilities on Home editions of windows: http://blogs.technet.com/b/fdcc/archive/2008/05/07/lgpo-utilities.aspx)