[signin] Enforce that either Dice or Mirror is enabled

Change-Id: I55ddd99da9115affc449f4f2f9fb5a0539c1171a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1924477
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: Monica Basta <msalama@chromium.org>
Cr-Commit-Position: refs/heads/master@{#717671}

chrome/browser/signin/account_consistency_mode_manager_unittest.cc

@@ -58,12 +58,7 @@ TEST(AccountConsistencyModeManagerTest, DefaultValue) {
   EXPECT_TRUE(
       AccountConsistencyModeManager::IsDiceEnabledForProfile(profile.get()));
 #else
-  EXPECT_EQ(signin::AccountConsistencyMethod::kDisabled,
-            AccountConsistencyModeManager::GetMethodForProfile(profile.get()));
-  EXPECT_FALSE(
-      AccountConsistencyModeManager::IsMirrorEnabledForProfile(profile.get()));
-  EXPECT_FALSE(
-      AccountConsistencyModeManager::IsDiceEnabledForProfile(profile.get()));
+#error Either Dice or Mirror should be enabled
 #endif
 }