ProfileSyncServiceHarness: don't sign in if already signed in

Changing the refresh token causes Sync (ServerConnectionManager in
particular) to mark the current access token as invalid. Since tests
typically always hand out the same access token string, any new access
token acquired later would also be considered invalid.

This was exposed by https://crrev.com/c/1148392, but the problem existed
all along.

Bug: 856179
Change-Id: I47e695e2415252281404b4e6e6170667ecf8180d
Reviewed-on: https://chromium-review.googlesource.com/1156595Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579410}

chrome/browser/sync/test/integration/profile_sync_service_harness.cc

@@ -174,14 +174,24 @@ bool ProfileSyncServiceHarness::SetupSync(syncer::ModelTypeSet synced_datatypes,
       return false;
     }
   } else if (signin_type_ == SigninType::FAKE_SIGNIN) {
-    // Authenticate sync client using GAIA credentials.
-    // TODO(https://crbug.com/814307): This ideally should go through
-    // identity_test_utils.h (and in the long run IdentityTestEnvironment), but
-    // making that change is complex for reasons described in the bug.
     identity::IdentityManager* identity_manager =
         IdentityManagerFactory::GetForProfile(profile_);
+    if (identity_manager->HasPrimaryAccountWithRefreshToken()) {
+      // Don't sign in again if we're already signed in. The reason is that
+      // changing the refresh token causes Sync (ServerConnectionManager in
+      // particular) to mark the current access token as invalid. Since tests
+      // typically always hand out the same access token string, any new access
+      // token acquired later would also be considered invalid.
+      DCHECK_EQ(identity_manager->GetPrimaryAccountInfo().gaia, gaia_id_);
+      DCHECK_EQ(identity_manager->GetPrimaryAccountInfo().email, username_);
+    } else {
+      // Authenticate sync client using GAIA credentials.
+      // TODO(https://crbug.com/814307): This ideally should go through
+      // identity_test_utils.h (and in the long run IdentityTestEnvironment),
+      // but making that change is complex for reasons described in the bug.
       identity_manager->SetPrimaryAccountSynchronouslyForTests(
           gaia_id_, username_, GenerateFakeOAuth2RefreshTokenString());
+    }
   } else {
     LOG(ERROR) << "Unsupported profile signin type.";
   }