Recent updates to Google Chrome have broken functionality in Microsoft Exchange OWA.  The below is a temporary fix until Microsoft releases an update.

Until May 2015, a registry workaround is available to restore the showModalDialog() method. To enable the showModalDialog() method, the following steps can be used:

1. Download ADM Policy Templates for Windows (if you want just the US English one, grab this chrome.zip)
2. Extract the downloaded files, then navigate to Start | Run: gpedit.msc
3. Navigate to Local Computer Policy | Computer Configuration | Administrative Templates
4. Right-click Administrative Templates and select Add/Remove Templates
5. Add the downloaded chrome.adm templates of Windows via the dialog for the specific language (English is EN-US)
6. Once the template is added, a Google Chrome folder will appear under ‘Classic Administrative Templates’
7. Select EnableDeprecatedWebPlatformFeatures setting in the right column. Right-click the setting and select Edit
8. Edit the EnableDeprecatedWebPlatformFeatures as shown below:
   1. Paste in the following string value: ShowModalDialog_EffectiveUntil20150430
   2. Click OK on the Show Contents dialog
   3. Click Apply and OK on the Enabled Deprecated Webplatform Features dialog
9. Restart the Google Chrome browser and type chrome://policy in the address bar
10. You should observe that this deprecated feature is now enabled.