Include fallback content for loading state.

app/assets/javascripts/issuable_time_tracker.js.es6

@@ -109,7 +109,7 @@
       },
     },
     template: `
-        <div class='time-tracking-component-wrap'>
+        <div class='time-tracking-component-wrap' v-cloak>
           <div class='sidebar-collapsed-icon'>
             <div class='time-tracking-collapsed-summary'>
               <div class='compare' v-if='showComparison'>

app/views/shared/issuable/_sidebar.html.haml

@@ -76,6 +76,9 @@
       - if issuable.has_attribute?(:time_estimate)
         #issuable-time-tracker.block
           %issuable-time-tracker{ ':time_estimate' => 'issuable.time_estimate', ':time_spent' => 'issuable.time_spent' }
+            .title.hide-collapsed
+              Time tracking
+              = icon('spinner spin')
       - if issuable.has_attribute?(:due_date)
         .block.due_date
           .sidebar-collapsed-icon