Disable sync for Lightspeed experimentation.

chrome/browser/sync/profile_sync_service_factory.cc

Index: chrome/browser/sync/profile_sync_service_factory.cc
diff --git a/chrome/browser/sync/profile_sync_service_factory.cc b/chrome/browser/sync/profile_sync_service_factory.cc
index 33bb0c675422cbe253b57b8b7264dde3887cb84c..212d07856332eb1fb494d28b811b6c73f01abd33 100644
--- a/chrome/browser/sync/profile_sync_service_factory.cc
+++ b/chrome/browser/sync/profile_sync_service_factory.cc
@@ -32,6 +32,7 @@
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "components/signin/core/browser/profile_oauth2_token_service.h"
 #include "components/signin/core/browser/signin_manager.h"
+#include "components/variations/variations_associated_data.h"
 #include "url/gurl.h"
 
 #if defined(ENABLE_EXTENSIONS)
@@ -50,6 +51,15 @@ ProfileSyncService* ProfileSyncServiceFactory::GetForProfile(
   if (!ProfileSyncService::IsSyncEnabled())
     return NULL;
 
+  // Disable sync experimentally to measure impact on startup time. Supervised
+  // users are unaffected, since supervised users rely completely on sync.
+  // TODO(mlerman): Remove this after the experiment. crbug.com/454788
+  if (!profile->IsSupervised() &&
+      !variations::GetVariationParamValue("LightSpeed", "DisableSync")
+           .empty()) {
+    return NULL;
+  }
+
   return static_cast<ProfileSyncService*>(
       GetInstance()->GetServiceForBrowserContext(profile, true));
 }