[unified-consent] Fix recording of revoke reason kUserSignedOut

The revoke reason kUserSignedOut should only be recorded when
the user opted into unified consent before. This CL fixes this.

Bug: 868892
Change-Id: I746ca040a554ec78599f16871e831acc11c7afcf
Reviewed-on: https://chromium-review.googlesource.com/1238583Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593515}

components/unified_consent/unified_consent_service.cc

@@ -298,9 +298,11 @@ void UnifiedConsentService::OnServiceStateChanged(Service service) {
 void UnifiedConsentService::OnPrimaryAccountCleared(
     const AccountInfo& account_info) {
   // When signing out, the unfied consent is revoked.
-  pref_service_->SetBoolean(prefs::kUnifiedConsentGiven, false);
-  RecordUnifiedConsentRevoked(
-      metrics::UnifiedConsentRevokeReason::kUserSignedOut);
+  if (IsUnifiedConsentGiven()) {
+    SetUnifiedConsentGiven(false);
+    RecordUnifiedConsentRevoked(
+        metrics::UnifiedConsentRevokeReason::kUserSignedOut);
+  }
 
   // By design, signing out of Chrome automatically disables off-by-default
   // services.