AU: Resume interrupted update attempts.

BUG=7390,7520
TEST=unit tests

Change-Id: I9baf72aa444dd855409f865f03fb665e91f8d03d

Review URL: http://codereview.chromium.org/3620013
diff --git a/generate_delta_main.cc b/generate_delta_main.cc
index 8c5d6a9..a113e15 100644
--- a/generate_delta_main.cc
+++ b/generate_delta_main.cc
@@ -91,6 +91,7 @@
       CHECK_EQ(performer.Write(&buf[0], bytes_read), bytes_read);
     }
     CHECK_EQ(performer.Close(), 0);
+    DeltaPerformer::ResetUpdateProgress(&prefs, false);
     LOG(INFO) << "done applying delta.";
     return 0;
   }