update toc experience.

Author: csyonghe

docs/_layouts/stdlib-reference.html

@@ -315,7 +315,12 @@
     var pageName = path.substr(firstSlash);
     var dotLoc = pageName.lastIndexOf(".");
     if (dotLoc == -1)
+    {
       dotLoc = pageName.length;
+      if (!pageName.endsWith("/"))
+        pageName += "/";
+      pageName += "index";
+    }
     var currentPageID = pageName.substr(0, dotLoc);
 
     var tocLists = document.getElementsByClassName("toc_root_list");
@@ -356,8 +361,20 @@
         curItem.getAttribute("class").startsWith("toc_root_list"))
         break;
     }
+    // Restore scrollbar position.
+    window.onbeforeunload = function() {
+        window.name = window.scrollY;
+    };
+    if (window.name.length() != 0)
+    {
+      var lastScrollPosition = parseInt(window.name);
+      tocColumn.scroll(0, lastScrollPosition);
+    }
+    // Ensure the selected item is visible.
     if (selectedItem != null)
+    {
       selectedItem.scrollIntoView(true);
+    }
     var subItems = selectedItem.getElementsByTagName("li");
     var subSectionTitles = [];
     var subSectionTitleStrs = [];