trivial speed-ups for the single editor case

edit/sections.js

@@ -455,6 +455,9 @@ function removeAreaAndSetDirty(area) {
 }
 
 function makeSectionVisible(cm) {
+  if (editors.length === 1) {
+    return;
+  }
   const section = cm.getSection();
   const bounds = section.getBoundingClientRect();
   if (

edit/source-editor.js

@@ -146,6 +146,8 @@ function createSourceEditor(style) {
     CodeMirror.commands.nextEditor = cm => nextPrevMozDocument(cm, 1);
     CodeMirror.commands.toggleStyle = toggleStyle;
     CodeMirror.commands.save = save;
+
+    CodeMirror.closestVisible = () => cm;
   }
 
   function updateMeta() {