Bug 1797836 - Part 3: Add a new AREA_ADDONS for the Unified Extensions panel. r=Gijs

This area doesn't have any special rules applied yet, nor can it have items moved to
it except programmatically. All of that will come later, including tests.

Differential Revision: https://phabricator.services.mozilla.com/D161079

browser/base/content/browser-addons.js

@@ -1543,6 +1543,13 @@ var gUnifiedExtensions = {
       );
       template.replaceWith(template.content);
       this._panel = document.getElementById("unified-extensions-panel");
+      let customizationArea = this._panel.querySelector(
+        "#unified-extensions-area"
+      );
+      CustomizableUI.registerPanelNode(
+        customizationArea,
+        CustomizableUI.AREA_ADDONS
+      );
       CustomizableUI.addPanelCloseListeners(this._panel);
     }
     return this._panel;

browser/components/customizableui/CustomizableUI.jsm

@@ -243,6 +243,16 @@ var CustomizableUIInternal = {
       true
     );
 
+    this.registerArea(
+      CustomizableUI.AREA_ADDONS,
+      {
+        type: CustomizableUI.TYPE_PANEL,
+        defaultPlacements: [],
+        anchor: "unified-extensions-button",
+      },
+      false
+    );
+
     let navbarPlacements = [
       "back-button",
       "forward-button",
@@ -321,6 +331,7 @@ var CustomizableUIInternal = {
     return new Set([
       ...this._builtinToolbars,
       CustomizableUI.AREA_FIXED_OVERFLOW_PANEL,
+      CustomizableUI.AREA_ADDONS,
     ]);
   },
 
@@ -3602,7 +3613,10 @@ var CustomizableUI = {
    * Constant reference to the ID of the non-dymanic (fixed) list in the overflow panel.
    */
   AREA_FIXED_OVERFLOW_PANEL: "widget-overflow-fixed-list",
-
+  /**
+   * Constant reference to the ID of the addons area.
+   */
+  AREA_ADDONS: "unified-extensions-area",
   /**
    * Constant indicating the area is a panel.
    */

browser/components/customizableui/content/panelUI.inc.xhtml

@@ -85,6 +85,10 @@
           <!-- overflowed extension buttons from the nav-bar will go here -->
         </vbox>
 
+        <vbox class="panel-subview-body" id="unified-extensions-area">
+          <!-- default area for extension browser action buttons -->
+        </vbox>
+
         <vbox class="panel-subview-body unified-extensions-list">
           <!-- active visible extensions go here -->
         </vbox>