Access Context Auditing: Move feature flag guard in service factory

Adjusts the placement of the Access Context Auditing feature flag guard
in the service factory to prevent erroneous instantiation of the service.

Bug: 1083384
Change-Id: I93872191a59e6a48be06044ec71b0d403a3738d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2249960Reviewed-by: Martin Šrámek <msramek@chromium.org>
Commit-Queue: Theodore Olsauskas-Warren <sauski@google.com>
Cr-Commit-Position: refs/heads/master@{#779371}

chrome/browser/browsing_data/access_context_audit_service_factory.cc

@@ -23,17 +23,17 @@ AccessContextAuditServiceFactory::GetInstance() {
 
 AccessContextAuditService* AccessContextAuditServiceFactory::GetForProfile(
     Profile* profile) {
-  if (profile->IsOffTheRecord() ||
-      !base::FeatureList::IsEnabled(
-          features::kClientStorageAccessContextAuditing))
-    return nullptr;
-
   return static_cast<AccessContextAuditService*>(
       GetInstance()->GetServiceForBrowserContext(profile, true));
 }
 
 KeyedService* AccessContextAuditServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
+  if (context->IsOffTheRecord() ||
+      !base::FeatureList::IsEnabled(
+          features::kClientStorageAccessContextAuditing))
+    return nullptr;
+
   std::unique_ptr<AccessContextAuditService> context_audit_service(
       new AccessContextAuditService());
   if (!context_audit_service->Init(