Add a custom element to own structure of shadow DOM plugin placeholders.

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) {
+    PluginPlaceholderElementPrototype.createCallback = function() {
+        // Produces DOM roughly equivalent to the following HTML:
+        //
+        // <div id="plugin-placeholder">
+        //   <div id="plugin-placeholder-content">
+        //     <div id="plugin-placeholder-message"></div>
+        //   </div>
+        // </div>
+        //
+        // FIXME: Move style out of script and into CSS.
+
+        this.id = 'plugin-placeholder';
+        this.style.width = '100%';
+        this.style.height = '100%';
+        this.style.overflow = 'hidden';
+        this.style.display = 'flex';
+        this.style.alignItems = 'center';
+        this.style.backgroundColor = 'gray';
+        this.style.font = '12px -webkit-control';
+
+        var contentElement = document.createElement('div');
+        contentElement.id = 'plugin-placeholder-content';
+        contentElement.style.textAlign = 'center';
+        contentElement.style.margin = 'auto';
+
+        var messageElement = document.createElement('div');
+        messageElement.id = 'plugin-placeholder-message';
+
+        contentElement.appendChild(messageElement);
+        this.appendChild(contentElement);
+
+        this.messageElement = messageElement;
+    };
+
+    Object.defineProperty(PluginPlaceholderElementPrototype, 'message', {
+        get: function() { return this.messageElement.innerHTML; },

[esprehn, 2014/09/02 23:12:00]

no innerHTML should be exposed like this.

+        set: function(html) { this.messageElement.innerHTML = html; },
+    });
+});