Apply 'disappearing messages disabled' icon.

Signal/Images.xcassets/system_message_disappearing_messages_disabled.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "timer-disabled-20@1x.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "timer-disabled-20@2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "timer-disabled-20@3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

Signal/src/ViewControllers/ConversationView/Cells/OWSSystemMessageCell.m

@@ -239,9 +239,16 @@ typedef void (^SystemMessageActionBlock)(void);
             case TSInfoMessageTypeGroupQuit:
                 return nil;
             case TSInfoMessageTypeDisappearingMessagesUpdate: {
-                //                OWSDisappearingConfigurationUpdateInfoMessage *configurationUpdate =
-                //                (OWSDisappearingConfigurationUpdateInfoMessage *)interaction; configurationIsEnabled
-                result = [UIImage imageNamed:@"system_message_disappearing_messages"];
+                BOOL areDisappearingMessagesEnabled = YES;
+                if ([interaction isKindOfClass:[OWSDisappearingConfigurationUpdateInfoMessage class]]) {
+                    areDisappearingMessagesEnabled
+                        = ((OWSDisappearingConfigurationUpdateInfoMessage *)interaction).configurationIsEnabled;
+                } else {
+                    OWSFail(@"%@ unexpected interaction type: %@", self.logTag, interaction.class);
+                }
+                result = (areDisappearingMessagesEnabled
+                        ? [UIImage imageNamed:@"system_message_disappearing_messages"]
+                        : [UIImage imageNamed:@"system_message_disappearing_messages_disabled"]);
                 break;
             }
             case TSInfoMessageVerificationStateChange: