sync: Add --enable-sync-sessions-v2 and necessary plumbing to use SessionsSyncManager.

chrome/browser/prerender/prerender_field_trial.cc

Index: chrome/browser/prerender/prerender_field_trial.cc
diff --git a/chrome/browser/prerender/prerender_field_trial.cc b/chrome/browser/prerender/prerender_field_trial.cc
index 3813c5f9e14603716bab4184c50e03f51737d320..52e63b54d958428470040425c724c7e8bcdaced7 100644
--- a/chrome/browser/prerender/prerender_field_trial.cc
+++ b/chrome/browser/prerender/prerender_field_trial.cc
@@ -320,7 +320,7 @@ string GetLocalPredictorSpecValue(string spec_key) {
 bool IsUnencryptedSyncEnabled(Profile* profile) {
   ProfileSyncService* service = ProfileSyncServiceFactory::GetInstance()->
       GetForProfile(profile);
-  return service && service->GetSessionModelAssociator() &&
+  return service && service->GetOpenTabsUIDelegate() &&
       !service->EncryptEverythingEnabled();
 }