Populate conversation snippet for timer updates

_locales/en/messages.json

@@ -432,5 +432,15 @@
     "timerOption_1_week_abbreviated": {
       "message": "1w",
       "description": "Label for a selectable option in the message expiration timer menu"
+    },
+    "timerSetTo": {
+      "message": "Timer set to $time$",
+      "description": "Displayed in the conversation list when the timer is updated.",
+      "placeholders": {
+        "time": {
+          "content": "$1",
+          "example": "1w"
+        }
+      }
     }
 }

js/models/messages.js

@@ -81,6 +81,13 @@
             if (this.get('attachments').length > 0) {
                 return i18n('mediaMessage');
             }
+            if (this.isExpirationTimerUpdate()) {
+                return i18n('timerSetTo',
+                    Whisper.ExpirationTimerOptions.getAbbreviated(
+                      this.get('expirationTimerUpdate').expireTimer
+                    )
+                );
+            }
 
             return '';
         },