Revert "Go back from Webkit to IE render engine"

This reverts commit f58ef0dcb6.

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/JsDialogHandler.cs

@@ -0,0 +1,36 @@
+// Copyright © 2010-2017 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+using CefSharp;
+
+namespace QuickLook.Plugin.HtmlViewer
+{
+    public class JsDialogHandler : IJsDialogHandler
+    {
+        public bool OnJSDialog(IWebBrowser browserControl, IBrowser browser, string originUrl,
+            CefJsDialogType dialogType, string messageText, string defaultPromptText, IJsDialogCallback callback,
+            ref bool suppressMessage)
+        {
+            return true;
+        }
+
+        public bool OnJSBeforeUnload(IWebBrowser browserControl, IBrowser browser, string message, bool isReload,
+            IJsDialogCallback callback)
+        {
+            //NOTE: No need to execute the callback if you return false
+            // callback.Continue(true);
+
+            //NOTE: Returning false will trigger the default behaviour, you need to return true to handle yourself.
+            return true;
+        }
+
+        public void OnResetDialogState(IWebBrowser browserControl, IBrowser browser)
+        {
+        }
+
+        public void OnDialogClosed(IWebBrowser browserControl, IBrowser browser)
+        {
+        }
+    }
+}