Avoid auth triggers if we haven't yet received the initial user.

#2078 altered the
initial state of currentUser from undefined to not undefined, which
caused the if statement to unconditionally evaluate to true. This
results in a race condition that could cause some initial writes to the
database to be dropped.

Fixes #2135

Author: rsgowman

packages/firestore/src/api/credentials.ts

@@ -135,6 +135,7 @@ export class FirebaseCredentialsProvider implements CredentialsProvider {
 
   /** Tracks the current User. */
   private currentUser: User = User.UNAUTHENTICATED;
+  private receivedInitialUser: boolean = false;
 
   /**
    * Counter used to detect if the token changed while a getToken request was
@@ -151,6 +152,7 @@ export class FirebaseCredentialsProvider implements CredentialsProvider {
     this.tokenListener = () => {
       this.tokenCounter++;
       this.currentUser = this.getUser();
+      this.receivedInitialUser = true;
       if (this.changeListener) {
         this.changeListener(this.currentUser);
       }
@@ -210,7 +212,7 @@ export class FirebaseCredentialsProvider implements CredentialsProvider {
     this.changeListener = changeListener;
 
     // Fire the initial event, but only if we received the initial user
-    if (this.currentUser) {
+    if (this.receivedInitialUser) {
       changeListener(this.currentUser);
     }
   }