[Sync] SyncEngine 1.5: Fix all backend references in PSS.

components/precache/content/precache_manager.cc

Index: components/precache/content/precache_manager.cc
diff --git a/components/precache/content/precache_manager.cc b/components/precache/content/precache_manager.cc
index f4333c12d64e9b02779ca6a8de304a99f2e8bcf5..327fa2b6b83ceafdd748f932467358cb30803ee7 100644
--- a/components/precache/content/precache_manager.cc
+++ b/components/precache/content/precache_manager.cc
@@ -99,7 +99,7 @@ bool PrecacheManager::IsPrecachingAllowed() const {
 }
 
 PrecacheManager::AllowedType PrecacheManager::PrecachingAllowed() const {
-  if (!(sync_service_ && sync_service_->IsBackendInitialized()))
+  if (!(sync_service_ && sync_service_->IsEngineInitialized()))
     return AllowedType::PENDING;
 
   // SyncService delegates to SyncPrefs, which must be called on the UI thread.
@@ -182,7 +182,7 @@ void PrecacheManager::OnGetUnfinishedWorkDone(
     }
   } else {
     if (PrecachingAllowed() != AllowedType::PENDING) {
-      // We are not waiting on the sync backend to be initialized. The user
+      // We are not waiting on the sync engine to be initialized. The user
       // either is not in the field trial, or does not have sync enabled.
       // Pretend that precaching started, so that the PrecacheServiceLauncher
       // doesn't try to start it again.