separating background apis to their own classes

src/background/windows.background.ts

@@ -0,0 +1,23 @@
+import MainBackground from './main.background';
+
+export default class WindowsBackground {
+    private windows: any;
+
+    constructor(private main: MainBackground) {
+        this.windows = chrome.windows;
+    }
+
+    async init() {
+        if (!this.windows) {
+            return;
+        }
+
+        this.windows.onFocusChanged.addListener(async (windowId: any) => {
+            if (windowId === null || windowId < 0) {
+                return;
+            }
+
+            await this.main.refreshBadgeAndMenu();
+        });
+    }
+}