Merge branch 'MAGETWO-34929' of github.corp.ebay.com:magento-webdev/magento2ce into MAGETWO-34929

Author: Oleg Zinoviev

app/design/adminhtml/Magento/backend/Magento_Backend/web/css/source/module/_menu.less

@@ -66,8 +66,8 @@
     }
     &._fixed {
         left: 0;
-        top: 0;
         position: fixed;
+        top: 0;
         ~ .page-wrapper {
             margin-left: @menu__width;
         }
@@ -205,8 +205,8 @@
             padding: @submenu__padding-vertical 0 0;
             position: absolute;
             top: -@menu-logo__outer-size;
-            transition-property: left, visibility;
             transition-duration: .5s;
+            transition-property: left, visibility;
             transition-timing-function: ease;
             visibility: hidden;
             z-index: @submenu__z-index;

app/design/adminhtml/Magento/backend/web/js/theme.js

@@ -14,59 +14,70 @@ define('globalNavigationScroll', [
         winHeight,
         menuHeight = menu.height(),
         menuHeightRest = 0,
+        menuScrollMax = 0,
         contentHeight,
         winTop = 0,
         winTopLast = 0,
         scrollStep = 0,
         nextTop = 0,
         fixedClass = '_fixed';
 
+    /**
+     * Check if menu is fixed
+     * @returns {boolean}
+     */
     function isMenuFixed() {
         return (menuHeight < contentHeight) && (contentHeight > winHeight);
     }
 
+    /**
+     * Add fixed menu class
+     * @param {jQuery} el
+     */
     function addFixed(el) {
         if (!el.hasClass(fixedClass)) {
             el.addClass(fixedClass);
         }
     }
 
+    /**
+     * Remove fixed menu class
+     * @param {jQuery} el
+     */
     function removeFixed(el) {
         if (el.hasClass(fixedClass)) {
             el.removeClass(fixedClass);
         }
     }
 
+    /**
+     * Calculate and apply menu position
+     */
     function positionMenu() {
 
-        //  Spot positions and heights
+        //  Spotting positions and heights
         winHeight = win.height();
         contentHeight = content.height();
         winTop = win.scrollTop();
-        scrollStep = winTop - winTopLast; // scroll step
-        menuHeightRest = menuHeight - winTop; // visible menu height
+        scrollStep = winTop - winTopLast;
+        menuHeightRest = menuHeight - winTop; // is a visible menu height
 
-        // Fixed menu cases
-        if (isMenuFixed()) {
+        if (isMenuFixed()) { // fixed menu cases
 
             addFixed(menu);
 
-            //  Smart scroll cases
-            if (menuHeight > winHeight) {
+            if (menuHeight > winHeight) { // smart scroll cases
 
-                //  Scroll down
-                if (winTop > winTopLast) {
+                if (winTop > winTopLast) { //  scroll down
 
-                    var menuScrollMax = menuHeight - winHeight;
+                    menuScrollMax = menuHeight - winHeight;
 
                     nextTop < (menuScrollMax - scrollStep) ?
                         nextTop += scrollStep : nextTop = menuScrollMax;
 
                     menu.css('top', -nextTop);
 
-                }
-                //  Scroll up
-                else if (winTop < winTopLast) {
+                } else if (winTop < winTopLast) { // scroll up
 
                     nextTop > -scrollStep ?
                         nextTop += scrollStep : nextTop = 0;
@@ -76,8 +87,8 @@ define('globalNavigationScroll', [
                 }
 
             }
-            //  Static menu cases
-        } else {
+
+        } else { // static menu cases
             removeFixed(menu);
         }
 
@@ -86,8 +97,7 @@ define('globalNavigationScroll', [
 
     }
 
-    //  Page start calculation
-    positionMenu();
+    positionMenu(); // page start calculation
 
     //  Change position on scroll
     win.on('scroll', function () {
@@ -99,9 +109,7 @@ define('globalNavigationScroll', [
         winHeight = win.height();
 
         //  Reset position if fixed and out of smart scroll
-        if (
-            (menuHeight < contentHeight) && (menuHeight <= winHeight)
-        ) {
+        if ((menuHeight < contentHeight) && (menuHeight <= winHeight)) {
             menu.removeAttr('style');
         }