Make addon-enabled as a clean architecture

src/content/client/AddonIndicatorClient.ts

@@ -0,0 +1,16 @@
+import * as messages from '../../shared/messages';
+
+export default interface AddonIndicatorClient {
+  setEnabled(enabled: boolean): Promise<void>;
+
+  // eslint-disable-next-line semi
+}
+
+export class AddonIndicatorClientImpl implements AddonIndicatorClient {
+  setEnabled(enabled: boolean): Promise<void> {
+    return browser.runtime.sendMessage({
+      type: messages.ADDON_ENABLED_RESPONSE,
+      enabled,
+    });
+  }
+}