make installEditorScheme() protected to support temporary editor schemes

platform/platform-impl/src/com/intellij/ide/ui/laf/UIThemeBasedLookAndFeelInfo.java

-// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.ide.ui.laf;
 
 import com.intellij.ide.ui.UITheme;
@@ -60,7 +60,7 @@ public class UIThemeBasedLookAndFeelInfo extends UIManager.LookAndFeelInfo {
     return myInitialised;
   }
 
-  private void installEditorScheme() {
+  protected void installEditorScheme() {
     String name = myTheme.getEditorSchemeName();
     if (name != null) {
       EditorColorsManager cm = EditorColorsManager.getInstance();