[Remoting] Make OAuthTokenGetter::TokenCallback OnceCallback

This CL makes OAuthTokenGetter::TokenCallback OnceCallback so that it's
cleaner to use. It also marks
OAuthTokenGetter::CredentialsUpdatedCallback repeating callback, which
doesn't change its behavior but makes it cleaner.

Bug: 824488
Change-Id: I7b5a64c66792ac32b01d788f1e4e2895d97a393a
Reviewed-on: https://chromium-review.googlesource.com/c/1477924
Commit-Queue: Yuwei Huang <[email protected]>
Reviewed-by: Joe Downing <[email protected]>
Cr-Commit-Position: refs/heads/master@{#633930}
diff --git a/remoting/ios/facade/ios_oauth_token_getter.h b/remoting/ios/facade/ios_oauth_token_getter.h
index 7ad1fa8..684f25d 100644
--- a/remoting/ios/facade/ios_oauth_token_getter.h
+++ b/remoting/ios/facade/ios_oauth_token_getter.h
@@ -20,7 +20,7 @@
   ~IosOauthTokenGetter() override;
 
   // OAuthTokenGetter overrides.
-  void CallWithToken(const TokenCallback& on_access_token) override;
+  void CallWithToken(TokenCallback on_access_token) override;
   void InvalidateCache() override;
 
   base::WeakPtr<IosOauthTokenGetter> GetWeakPtr();