DevTools: add entry points for command menu

third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 471 matching lines @@
     else
       constraints = constraints.addHeight(new UI.Constraints(new UI.Size(0, 30)));
     return constraints;
   }
 
   _updateTabElements() {
     UI.invokeOnceAfterBatchUpdate(this, this._innerUpdateTabElements);
   }
 
   /**
-   * @param {string} text
+   * @param {!Element} element
    */
-  setPlaceholderText(text) {
-    this._noTabsMessage = text;
+  setPlaceholderElement(element) {
+    this._noTabsMessageElement = element;
+    element.classList.add('fill');

[pfeldman, 2017/03/28 00:59:35]

You should not add classes to provided elements - they might be incompatible
with the ones you set. Either defer to placeholder to position itself or
introduce intermediate container.

Overall, keeping it in light dom might be not the best idea - there is now no
way placeholders are consistent.

[luoe, 2017/04/22 00:07:03]

Consistency sounds great to me, I'll keep it in the shadow.

   }
 
   _innerUpdateTabElements() {
     if (!this.isShowing())
       return;
 
     if (!this._tabs.length) {
       this._contentElement.classList.add('has-no-tabs');
-      if (this._noTabsMessage && !this._noTabsMessageElement) {
-        this._noTabsMessageElement = this._contentElement.createChild('div', 'tabbed-pane-placeholder fill');
-        this._noTabsMessageElement.textContent = this._noTabsMessage;
-      }
+      if (this._noTabsMessageElement)
+        this.element.appendChild(this._noTabsMessageElement);
     } else {
       this._contentElement.classList.remove('has-no-tabs');
-      if (this._noTabsMessageElement) {
+      if (this._noTabsMessageElement)
         this._noTabsMessageElement.remove();
-        delete this._noTabsMessageElement;
-      }
     }
 
     this._measureDropDownButton();
     this._updateWidths();
     this._updateTabsDropDown();
     this._updateTabSlider();
   }
 
   /**
    * @param {number} index
@@ skipping 698 matching lines @@
    * @param {!Array.<string>} ids
    */
   closeTabs(tabbedPane, ids) {},
 
   /**
    * @param {string} tabId
    * @param {!UI.ContextMenu} contextMenu
    */
   onContextMenu(tabId, contextMenu) {}
 };