Promote Apps Developer Tools in the chrome:extensions page

chrome/browser/resources/extensions/extensions.css

 /* Copyright (c) 2012 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. */
 
 html.loading * {
   -webkit-transition-duration: 0 !important;
 }
 
 html:not(.focus-outline-visible)
 :enabled:focus:-webkit-any(input[type='checkbox'], input[type='radio']) {
@@ skipping 23 matching lines @@
 
 #dev-controls .buttons-container {
   display: -webkit-box;
   padding-top: 13px;
 }
 
 #dev-controls button {
   white-space: nowrap;
 }
 
+#apps-developer-tools-promo {
+  -webkit-margin-before: 15px;
+  -webkit-padding-before: 5px;
+  align-items: center;
+  border-top: 1px solid #eee;
+  display: flex;
+  font-size: 13px;
+}
+
+#apps-developer-tools-promo img {
+  content: url(apps_developer_tools_promo_48.png);
+}
+
+#apps-developer-tools-promo-text,
+#apps-developer-tools-promo-link {
+  -webkit-margin-start: 5px;
+}
+
+#apps-developer-tools-promo-close-wrapper {
+  display: flex;
+  flex-grow: 1;
+  justify-content: flex-end;
+}
+
+#apps-developer-tools-promo .close-button {
+  background: url(chrome://theme/IDR_CLOSE_DIALOG) no-repeat center center;
+  height: 14px;
+  width: 14px;
+  z-index: 1;
+}
+
+#apps-developer-tools-promo .close-button:hover {
+  background-image: url(chrome://theme/IDR_CLOSE_DIALOG_H);
+}
+
+#apps-developer-tools-promo .close-button:active {
+  background-image: url(chrome://theme/IDR_CLOSE_DIALOG_P);
+}
+
 #extension-settings.dev-mode #dev-controls {
   -webkit-transition-duration: 250ms;
   height: 45px;
   opacity: 1;
   padding-bottom: 7px;
 }
 
+#extension-settings.dev-mode.adt-promo #dev-controls {
+  height: 105px;  /* Allow more height for the Apps Developer Tools promo. */
+}
+
 #dev-controls-spacer {
   -webkit-box-flex: 1;
 }
 
 #dev-toggle {
   margin-top: 0;
   text-align: end;
 }
 
 #extension-settings:not(.dev-mode) .developer-extras {
@@ skipping 19 matching lines @@
 
 #no-extensions-message {
   font-weight: bold;
 }
 
 #suggest-gallery {
   -webkit-padding-start: 10px;
 }
 
 #footer-section {
-  background: url('chrome://theme/IDR_WEBSTORE_ICON_32') no-repeat left center;
+  background: url(chrome://theme/IDR_WEBSTORE_ICON_32) no-repeat left center;
   font-size: 1.25em;
 }
 
 html[dir=rtl] #footer-section {
-  background: url('chrome://theme/IDR_WEBSTORE_ICON_32') no-repeat right center;
+  background: url(chrome://theme/IDR_WEBSTORE_ICON_32) no-repeat right center;
 }
 
 #footer-section > a {
   -webkit-margin-start: 42px;
   line-height: 32px;
 }
 
 .empty-extension-list {
   height: 3em;
 }
@@ skipping 204 matching lines @@
 }
 
 /* Managed mode */
 
 .page:not(.profile-is-managed) .profile-is-managed-banner,
 .profile-is-managed .more-extensions-link {
   display: none;
 }
 
 .profile-is-managed-banner .page-banner-text {
-  background-image: url('chrome://theme/IDR_WARNING');
+  background-image: url(chrome://theme/IDR_WARNING);
 }
 
 /* Sideload Wipeout */
 
 .sideload-wipeout-learn-more {
   text-decoration: none;
 }
 
 .sideload-wipeout-banner .page-banner-text {
   -webkit-padding-start: 8px;
   background-image: none;
 }