DevTools: introduce persistence/ module

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

Index: third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js b/third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js
index 4be39bdbe204a651beae8a89de3bbef4e83d3fa7..ab911b254a5caf922fc54c0b8d9e0ab926bbd189 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui/TabbedPane.js
@@ -94,6 +94,15 @@ WebInspector.TabbedPane.prototype = {
     },
 
     /**
+     * @param {string} tabId
+     * @return {number}
+     */
+    tabIndex: function(tabId)
+    {
+        return this._tabs.findIndex(tab => tab.id === tabId);
+    },
+
+    /**
      * @return {!Array.<!WebInspector.Widget>}
      */
     tabViews: function()