[MD settings] hide option for incognito on session only exceptions

chrome/browser/resources/settings/site_settings/add_site_dialog.js

Index: chrome/browser/resources/settings/site_settings/add_site_dialog.js
diff --git a/chrome/browser/resources/settings/site_settings/add_site_dialog.js b/chrome/browser/resources/settings/site_settings/add_site_dialog.js
index 1e02855c308c073244b3ab1c8fd7911eac45d034..41eecca19c87a1f0f710a7097fbe8d47d099c78f 100644
--- a/chrome/browser/resources/settings/site_settings/add_site_dialog.js
+++ b/chrome/browser/resources/settings/site_settings/add_site_dialog.js
@@ -26,7 +26,7 @@ Polymer({
     contentSetting: String,
 
     /** @private */
-    isIncognitoActive_: Boolean,
+    showIncognitoSessionOnly_: Boolean,
 
     /**
      * The site to add an exception for.
@@ -48,7 +48,8 @@ Polymer({
    */
   open: function(type) {
     this.addWebUIListener('onIncognitoStatusChanged', function(isActive) {
-      this.isIncognitoActive_ = isActive;
+      this.showIncognitoSessionOnly_ = isActive &&
+          this.contentSetting != settings.PermissionValues.SESSION_ONLY;
     }.bind(this));
     this.browserProxy.updateIncognitoStatus();
     this.$.dialog.showModal();