tab row widgetizing

src/public/javascripts/widgets/tab_aware_widget.js

@@ -0,0 +1,19 @@
+import BasicWidget from "./basic_widget.js";
+
+export default class TabAwareWidget extends BasicWidget {
+    constructor(appContext) {
+        super(appContext);
+
+        /** @var {TabContext} */
+        this.tabContext = null;
+    }
+
+    // to override
+    activeTabChanged() {}
+
+    activeTabChangedListener() {
+        this.tabContext = this.appContext.getActiveTabContext();
+
+        this.activeTabChanged();
+    }
+}