[Blink-in-JS] Migrate the PrivateScript specific methods/attributes to ScriptController

Source/core/html/shadow/PluginPlaceholderElement.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
-installClass('PluginPlaceholderElement', function(PluginPlaceholderElementPrototype) {
+privateScriptController.installClass('PluginPlaceholderElement', function(PluginPlaceholderElementPrototype) {
     // FIXME: Load this from a .css file.
     var styleSource =
         '#plugin-placeholder {' +
         '    all: initial;' +
         '    width: 100%;' +
         '    height: 100%;' +
         '    overflow: hidden;' +
         '    display: flex;' +
         '    align-items: center;' +
         '    background: gray;' +
@@ skipping 76 matching lines @@
     Object.defineProperty(PluginPlaceholderElementPrototype, 'message', {
         get: function() { return this.messageElement.textContent; },
         set: function(message) { this.messageElement.textContent = message; },
     });
 
     Object.defineProperty(PluginPlaceholderElementPrototype, 'closeable', {
         get: function() { return this.closeButton.style.display != 'none'; },
         set: function(closeable) { this.closeButton.style.display = closeable ? '' : 'none'; },
     });
 });