Fixes merge request bar styling when performance bar is visible

app/assets/javascripts/merge_request_tabs.js

@@ -73,6 +73,7 @@ export default class MergeRequestTabs {
   constructor({ action, setUrl, stubLocation } = {}) {
     const mergeRequestTabs = document.querySelector('.js-tabs-affix');
     const navbar = document.querySelector('.navbar-gitlab');
+    const peek = document.getElementById('peek');
     const paddingTop = 16;
 
     this.diffsLoaded = false;
@@ -86,6 +87,10 @@ export default class MergeRequestTabs {
     this.showTab = this.showTab.bind(this);
     this.stickyTop = navbar ? navbar.offsetHeight - paddingTop : 0;
 
+    if (peek) {
+      this.stickyTop += peek.offsetHeight;
+    }
+
     if (mergeRequestTabs) {
       this.stickyTop += mergeRequestTabs.offsetHeight;
     }