AU: Start checkpointing update progress.

delta_performer.h

Index: delta_performer.h
diff --git a/delta_performer.h b/delta_performer.h
index 82f4d90623cfa8087625139702f277a312dd0c17..2f9fd8a7906a9ee6e5dcc31dee202c55c3fdf864 100644
--- a/delta_performer.h
+++ b/delta_performer.h
@@ -17,13 +17,16 @@
 
 namespace chromeos_update_engine {
 
+class PrefsInterface;
+
 // This class performs the actions in a delta update synchronously. The delta
 // update itself should be passed in in chunks as it is received.
 
 class DeltaPerformer : public FileWriter {
  public:
-  DeltaPerformer()
-      : fd_(-1),
+  DeltaPerformer(PrefsInterface* prefs)
+      : prefs_(prefs),
+        fd_(-1),
         kernel_fd_(-1),
         manifest_valid_(false),
         next_operation_num_(0),
@@ -99,6 +102,12 @@ class DeltaPerformer : public FileWriter {
   // updates the hash calculator with these bytes before discarding them.
   void DiscardBufferHeadBytes(size_t count, bool do_hash);
 
+  bool ResetUpdateProgress();
+  bool CheckpointUpdateProgress();
+
+  // Update Engine preference store.
+  PrefsInterface* prefs_;
+
   // File descriptor of open device.
   int fd_;