DevTools: When no manifest detected, provide user with link to docs.

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._reportView = new UI.ReportView(Common.UIString('App Manifest'));
     this._reportView.show(this.contentElement);
 
     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);
 
+    this._manifestlessSection = this._reportView.appendSection(Common.UIString('No manifest detected'));
+    var p = createElement('p');
+    p.textContent = 'A web manifest allows you to control how your app behaves when launched and displayed to the user. ';
+    p.appendChild(UI.createExternalLink('https://developers.google.com/web/progressive-web-apps/?utm_source=devtools',
+        Common.UIString('Read more on developers.google.com')));
+    this._manifestlessSection.element.appendChild(p);
+    this._manifestlessSection.element.classList.add('hidden');
+
     this._presentationSection = this._reportView.appendSection(Common.UIString('Presentation'));
     this._iconsSection = this._reportView.appendSection(Common.UIString('Icons'));
 
     this._nameField = this._identitySection.appendField(Common.UIString('Name'));
     this._shortNameField = this._identitySection.appendField(Common.UIString('Short name'));
 
     this._startURLField = this._presentationSection.appendField(Common.UIString('Start URL'));
 
     var themeColorField = this._presentationSection.appendField(Common.UIString('Theme color'));
     this._themeColorSwatch = InlineEditor.ColorSwatch.create();
@@ skipping 47 matching lines @@
    */
   _renderManifest(url, data, errors) {
     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 = '{}';
+    var manifestDataFound = !!data;
+    this._manifestlessSection.element.classList.toggle('hidden', manifestDataFound);
+    this._presentationSection.element.classList.toggle('hidden', !manifestDataFound);
+    this._iconsSection.element.classList.toggle('hidden', !manifestDataFound);
+    this._identitySection.element.classList.toggle('hidden', !manifestDataFound);
+    if (!data) return;
 
     var parsedManifest = JSON.parse(data);
     this._nameField.textContent = stringProperty('name');
     this._shortNameField.textContent = stringProperty('short_name');
     this._startURLField.removeChildren();
     var startURL = stringProperty('start_url');
     if (startURL) {
       this._startURLField.appendChild(Components.Linkifier.linkifyURL(
           /** @type {string} */ (Common.ParsedURL.completeURL(url, startURL)), startURL));
     }
@@ skipping 36 matching lines @@
    * @param {!Common.Event} event
    */
   _addToHomescreen(event) {
     var target = SDK.targetManager.mainTarget();
     if (target && target.hasBrowserCapability()) {
       target.pageAgent().requestAppBanner();
       Common.console.show();
     }
   }
 };