comment changes

Author: Brian Chen

packages/firestore-types/index.d.ts

@@ -136,7 +136,8 @@ export class FirebaseFirestore {
   /**
    * Attempts to enable persistent storage, if possible.
    *
-   * Must be called before any other methods (other than settings()).
+   * Must be called before any other methods (other than settings() and
+   * clearPersistence()).
    *
    * If this fails, enablePersistence() will reject the promise it returns.
    * Note that even after this failure, the firestore instance will remain
@@ -217,7 +218,12 @@ export class FirebaseFirestore {
   app: any;
 
   /**
-   * Clears the persistence cache. This can only be called when the client is not running.
+   * Clears the persistent storage.
+   *
+   * Must be called after the app is shutdown or before other methods (other 
+   * than settings()). If the client is still running, an exception `code` will be thrown.
+   *
+   *   * failed-precondition: The app is still running in a browser tab.
    *
    * @return A promise that is resolved once the persistence has been cleared.
    */