[Sync] Move snapshot cache from SBHI to PSS.

components/sync/driver/glue/sync_backend_host_impl.h

Index: components/sync/driver/glue/sync_backend_host_impl.h
diff --git a/components/sync/driver/glue/sync_backend_host_impl.h b/components/sync/driver/glue/sync_backend_host_impl.h
index 0f33a9dd13bd3928199555edb0cf0c280cf81d83..4d062887fd467ef085633ca241d5b95e809ced7e 100644
--- a/components/sync/driver/glue/sync_backend_host_impl.h
+++ b/components/sync/driver/glue/sync_backend_host_impl.h
@@ -78,7 +78,6 @@ class SyncBackendHostImpl : public SyncEngine, public InvalidationHandler {
   void EnableEncryptEverything() override;
   UserShare* GetUserShare() const override;
   Status GetDetailedStatus() override;
-  SyncCycleSnapshot GetLastCycleSnapshot() const override;
   bool HasUnsyncedItems() const override;
   bool IsNigoriEnabled() const override;
   PassphraseType GetPassphraseType() const override;
@@ -289,9 +288,6 @@ class SyncBackendHostImpl : public SyncEngine, public InvalidationHandler {
   // first set (if available).
   base::Time cached_explicit_passphrase_time_;
 
-  // UI-thread cache of the last SyncCycleSnapshot received from syncapi.
-  SyncCycleSnapshot last_snapshot_;
-
   invalidation::InvalidationService* invalidator_;
   bool invalidation_handler_registered_ = false;