Main review cleanup

Author: schmidt-sebastian

packages/firestore/src/local/indexeddb_persistence.ts

@@ -110,20 +110,18 @@ export class IndexedDbPersistence implements Persistence {
   private serializer: LocalSerializer;
 
   constructor(prefix: string, serializer: JsonProtoSerializer) {
+    if (!IndexedDbPersistence.isAvailable()) {
+      throw new FirestoreError(
+          Code.UNIMPLEMENTED,
+          UNSUPPORTED_PLATFORM_ERROR_MSG
+      );
+    }
     this.dbName = prefix + IndexedDbPersistence.MAIN_DATABASE;
     this.serializer = new LocalSerializer(serializer);
     this.localStoragePrefix = prefix;
   }
 
   start(): Promise<void> {
-    if (!IndexedDbPersistence.isAvailable()) {
-      this.persistenceError = new FirestoreError(
-        Code.UNIMPLEMENTED,
-        UNSUPPORTED_PLATFORM_ERROR_MSG
-      );
-      return Promise.reject(this.persistenceError);
-    }
-
     assert(!this.started, 'IndexedDbPersistence double-started!');
     this.started = true;