sync: use progress markers instead of timestamps during GetUpdates

chrome/browser/sync/sessions/session_state.h

Index: chrome/browser/sync/sessions/session_state.h
diff --git a/chrome/browser/sync/sessions/session_state.h b/chrome/browser/sync/sessions/session_state.h
index aca18dcb1486919ae6817ce74a7ed90a5c5fed91..eb13ca2869233c737aac479b8d79a517bf4c5565 100644
--- a/chrome/browser/sync/sessions/session_state.h
+++ b/chrome/browser/sync/sessions/session_state.h
@@ -35,9 +35,13 @@ class UpdateProgress;
 // Data pertaining to the status of an active Syncer object.
 struct SyncerStatus {
   SyncerStatus()
-      : invalid_store(false), syncer_stuck(false),
-        syncing(false), num_successful_commits(0),
-        num_successful_bookmark_commits(0) {}
+      : invalid_store(false),
+        syncer_stuck(false),
+        syncing(false),
+        num_successful_commits(0),
+        num_successful_bookmark_commits(0),
+        num_updates_downloaded(0),
+        num_tombstone_updates_downloaded(0) {}
 
   // True when we get such an INVALID_STORE error from the server.
   bool invalid_store;
@@ -47,6 +51,10 @@ struct SyncerStatus {
   int num_successful_commits;
   // This is needed for monitoring extensions activity.
   int num_successful_bookmark_commits;
+
+  // Download event counters.

[tim (not reviewing), 2011/01/11 19:14:23]

It looks like you update the counters at the same time as we update the
'UpdateProgress', which is where the number of verified downloaded updates is
currently tracked (VerifiedUpdatesSize()). It is split up by model safe group, 
so you would need a function in StatusController to iterate and sum (similar to
what ComputeMaxLocalTimestamp did). UpdateProgress doesn't count the tombstones,
but we pass in the update to AddVerifyResult so it'd be trivial to add a
num_tombstone_updates_downloaded there.  And you could revert
verify_updates_command, I think.

[ncarter (slow), 2011/01/13 00:06:13]

Moving these to the UpdateProgress would require additional handling in
constructing the SyncSessionSnapshot.  I rather like that there's just one POD
field that gets incremented in one place, and plumbed through.  And, my goal for
these fields is for them to be durable across sessions, in which case the
ephemerality of UpdateProgress would make for an inappropriate place.

They can't go in the Context because the context is const.

+  int num_updates_downloaded;
+  int num_tombstone_updates_downloaded;
 };
 
 // Counters for various errors that can occur repeatedly during a sync session.
@@ -69,25 +77,26 @@ struct ErrorCounters {
 // An immutable snapshot of state from a SyncSession.  Convenient to use as
 // part of notifications as it is inherently thread-safe.
 struct SyncSessionSnapshot {
-  SyncSessionSnapshot(const SyncerStatus& syncer_status,
+  SyncSessionSnapshot(
+      const SyncerStatus& syncer_status,
       const ErrorCounters& errors,
       int64 num_server_changes_remaining,
-      int64 max_local_timestamp,
       bool is_share_usable,
       const syncable::ModelTypeBitSet& initial_sync_ended,
+      std::string download_progress_markers[syncable::MODEL_TYPE_COUNT],
       bool more_to_sync,
       bool is_silenced,
       int64 unsynced_count,
       int num_conflicting_updates,
-                      bool did_commit_items);
+      bool did_commit_items);
   ~SyncSessionSnapshot();
 
   const SyncerStatus syncer_status;
   const ErrorCounters errors;
   const int64 num_server_changes_remaining;
-  const int64 max_local_timestamp;
   const bool is_share_usable;
   const syncable::ModelTypeBitSet initial_sync_ended;
+  const std::string download_progress_markers[syncable::MODEL_TYPE_COUNT];
   const bool has_more_to_sync;
   const bool is_silenced;
   const int64 unsynced_count;
@@ -233,7 +242,7 @@ struct AllModelTypeState {
   ClientToServerResponse commit_response;
   // We GetUpdates for some combination of types at once.
   // requested_update_types stores the set of types which were requested.
-  syncable::MultiTypeTimeStamp updates_request_parameters;
+  syncable::ModelTypeBitSet updates_request_types;
   ClientToServerResponse updates_response;
   // Used to build the shared commit message.
   DirtyOnWrite<std::vector<int64> > unsynced_handles;
@@ -257,8 +266,6 @@ struct PerModelSafeGroupState {
 struct PerModelTypeState {
   explicit PerModelTypeState(bool* dirty_flag);
   ~PerModelTypeState();
-
-  DirtyOnWrite<int64> current_download_timestamp;
 };
 
 }  // namespace sessions