[DevTools] Show an empty Manifest view if no manifest

third_party/WebKit/Source/devtools/front_end/resources/AppManifestView.js

 // Copyright (c) 2016 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.
 /**
  * @implements {SDK.TargetManager.Observer}
  * @unrestricted
  */
 Resources.AppManifestView = class extends UI.VBox {
   constructor() {
     super(true);
     this.registerRequiredCSS('resources/appManifestView.css');
 
+    this._emptyView = new UI.EmptyWidget(Common.UIString('No web app manifest'));
+
+    this._emptyView.show(this.contentElement);
+    this._emptyView.hideWidget();
+
     this._reportView = new UI.ReportView(Common.UIString('App Manifest'));
     this._reportView.show(this.contentElement);
+    this._reportView.hideWidget();
 
     this._errorsSection = this._reportView.appendSection(Common.UIString('Errors and warnings'));
     this._identitySection = this._reportView.appendSection(Common.UIString('Identity'));
     var toolbar = this._identitySection.createToolbar();
     toolbar.renderAsLinks();
     var addToHomeScreen =
         new UI.ToolbarButton(Common.UIString('Add to homescreen'), undefined, Common.UIString('Add to homescreen'));
     addToHomeScreen.addEventListener(UI.ToolbarButton.Events.Click, this._addToHomescreen, this);
     toolbar.appendToolbarItem(addToHomeScreen);
 
@@ skipping 49 matching lines @@
   _updateManifest() {
     this._resourceTreeModel.fetchAppManifest(this._renderManifest.bind(this));
   }
 
   /**
    * @param {string} url
    * @param {?string} data
    * @param {!Array<!Protocol.Page.AppManifestError>} errors
    */
   _renderManifest(url, data, errors) {
+    if (!data && !errors.length) {
+      this._emptyView.showWidget();
+      this._reportView.hideWidget();
+      return;
+    }
+    this._emptyView.hideWidget();
+    this._reportView.showWidget();
+
     this._reportView.setURL(Components.Linkifier.linkifyURL(url));
     this._errorsSection.clearContent();
     this._errorsSection.element.classList.toggle('hidden', !errors.length);
     for (var error of errors) {
       this._errorsSection.appendRow().appendChild(
           UI.createLabel(error.message, error.critical ? 'smallicon-error' : 'smallicon-warning'));
     }
 
     if (!data)
       data = '{}';
@@ skipping 46 matching lines @@
    * @param {!Common.Event} event
    */
   _addToHomescreen(event) {
     var target = SDK.targetManager.mainTarget();
     if (target && target.hasBrowserCapability()) {
       target.pageAgent().requestAppBanner();
       Common.console.show();
     }
   }
 };