Change CredentialsProvider::TokenListener to use StatusOr<Token> (#945)

* Change CredentialsProvider::TokenListener to use StatusOr

Rather than a token plus error code/msg.

* Eliminate the concept of an invalid Token

Instead, we'll just use StatusOr<Token>. Note that unauthenticated
tokens are handled as a special case; they're created via:
  Token::Unauthenticated()
and are otherwise "valid", though attempting to retrieve the raw token
on one of these tokens will cause an assertion failure.

1 files changed, 2 insertions, 4 deletions

diff --git a/Firestore/core/test/firebase/firestore/auth/token_test.cc b/Firestore/core/test/firebase/firestore/auth/token_test.cc
index 8f784d6..e34053e 100644
--- a/Firestore/core/test/firebase/firestore/auth/token_test.cc
+++ b/Firestore/core/test/firebase/firestore/auth/token_test.cc
@@ -26,14 +26,12 @@ TEST(Token, Getter) {
   Token token("token", User("abc"));
   EXPECT_EQ("token", token.token());
   EXPECT_EQ(User("abc"), token.user());
-  EXPECT_TRUE(token.is_valid());
 }
 
-TEST(Token, InvalidToken) {
-  const Token& token = Token::Invalid();
+TEST(Token, UnauthenticatedToken) {
+  const Token& token = Token::Unauthenticated();
   EXPECT_ANY_THROW(token.token());
   EXPECT_EQ(User::Unauthenticated(), token.user());
-  EXPECT_FALSE(token.is_valid());
 }
 
 }  // namespace auth