AU: Start checkpointing update progress.

download_action.h

Index: download_action.h
diff --git a/download_action.h b/download_action.h
index f6d5a117418ede05a4808e955f67851fec321f79..62dd29afb51ddb069e30f806774f01f8a69101a9 100644
--- a/download_action.h
+++ b/download_action.h
@@ -49,6 +49,7 @@ class DownloadActionDelegate {
 
 class DownloadAction;
 class NoneType;
+class PrefsInterface;
 
 template<>
 class ActionTraits<DownloadAction> {
@@ -64,7 +65,7 @@ class DownloadAction : public Action<DownloadAction>,
   // Takes ownership of the passed in HttpFetcher. Useful for testing.
   // A good calling pattern is:
   // DownloadAction(new WhateverHttpFetcher);
-  DownloadAction(HttpFetcher* http_fetcher);
+  DownloadAction(PrefsInterface* prefs, HttpFetcher* http_fetcher);
   virtual ~DownloadAction();
   typedef ActionTraits<DownloadAction>::InputObjectType InputObjectType;
   typedef ActionTraits<DownloadAction>::OutputObjectType OutputObjectType;
@@ -96,6 +97,9 @@ class DownloadAction : public Action<DownloadAction>,
   // The InstallPlan passed in
   InstallPlan install_plan_;
 
+  // Update Engine preference store.
+  PrefsInterface* prefs_;
+
   // The FileWriter that downloaded data should be written to. It will
   // either point to *decompressing_file_writer_ or *delta_performer_.
   FileWriter* writer_;