Fix example code of PrimaryAccountAccessTokenFetcher

This example code is really useful, but it contained a few minor
C++ mistakes.

Bug: N/A
Test: compiled
Change-Id: If0b110c89657a4f018e2b406b0e4b2213a4fe420
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354594
Auto-Submit: Jeroen Dhollander <jeroendh@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803068}

components/signin/public/identity_manager/primary_account_access_token_fetcher.h

@@ -76,11 +76,11 @@ struct AccessTokenInfo;
 //       // Choose the mode in which to fetch the access token:
 //       // see AccessTokenFetcher::Mode below for definitions.
 //       auto mode =
-//         signin::PrimaryAccountAccessTokenFetcher::Mode::kWaitUntilAvailable;
+//         PrimaryAccountAccessTokenFetcher::Mode::kWaitUntilAvailable;
 
 //       // Create the fetcher.
 //       access_token_fetcher_ =
-//           std::make_unique<PrimaryAccountAccessTokenFetcher(
+//           std::make_unique<PrimaryAccountAccessTokenFetcher>(
 //               /*consumer_name=*/"MyClass",
 //               identity_manager_,
 //               scopes,
@@ -91,7 +91,7 @@ struct AccessTokenInfo;
 //                              mode);
 //
 //     }
-//     MyClass::OnAccessTokenRequestCompleted(
+//     void MyClass::OnAccessTokenRequestCompleted(
 //         GoogleServiceAuthError error, AccessTokenInfo access_token_info) {
 //       // It is safe to destroy |access_token_fetcher_| from this callback.
 //       access_token_fetcher_.reset();