Make issuable sidebar setSidebarHeight more efficient

1. Moves logic for setSidebarHeight into sidebar_height_manager to allow for better code sharing with bulk update sidebar.
2. Makes setSidebarHeight more efficient, by preventing its being called when sidebar state hasn't changed.

app/assets/javascripts/issuable_bulk_update_sidebar.js

@@ -5,6 +5,7 @@
 /* global SubscriptionSelect */
 
 import IssuableBulkUpdateActions from './issuable_bulk_update_actions';
+import SidebarHeightManager from './sidebar_height_manager';
 
 const HIDDEN_CLASS = 'hidden';
 const DISABLED_CONTENT_CLASS = 'disabled-content';
@@ -56,18 +57,6 @@ export default class IssuableBulkUpdateSidebar {
     return navbarHeight + layoutNavHeight + subNavScroll;
   }
 
-  initSidebar() {
-    if (!this.navHeight) {
-      this.navHeight = this.getNavHeight();
-    }
-
-    if (!this.sidebarInitialized) {
-      $(document).off('scroll').on('scroll', _.throttle(this.setSidebarHeight, 10).bind(this));
-      $(window).off('resize').on('resize', _.throttle(this.setSidebarHeight, 10).bind(this));
-      this.sidebarInitialized = true;
-    }
-  }
-
   setupBulkUpdateActions() {
     IssuableBulkUpdateActions.setOriginalDropdownData();
   }
@@ -97,7 +86,7 @@ export default class IssuableBulkUpdateSidebar {
     this.toggleCheckboxDisplay(enable);
 
     if (enable) {
-      this.initSidebar();
+      SidebarHeightManager.init();
     }
   }
 
@@ -143,17 +132,6 @@ export default class IssuableBulkUpdateSidebar {
       this.$bulkEditSubmitBtn.enable();
     }
   }
-  // loosely based on method of the same name in right_sidebar.js
-  setSidebarHeight() {
-    const currentScrollDepth = window.pageYOffset || 0;
-    const diff = this.navHeight - currentScrollDepth;
-
-    if (diff > 0) {
-      this.$sidebar.outerHeight(window.innerHeight - diff);
-    } else {
-      this.$sidebar.outerHeight('100%');
-    }
-  }
 
   static getCheckedIssueIds() {
     const $checkedIssues = $('.selected_issue:checked');