Make it clear what last_sync_timestamp actually tracks. Update

Make it clear what last_sync_timestamp actually tracks.  Update 
last_sync_timestamp from the new_timestamp only, never from per-entry 
timestamps.  Use what the server sends us to know whether or not there 
are more updates to fetch.  Eliminate some unnecessarily complicated
logic having to do with the # of updates returned -- that's always a red 
herring; with server-side filtering, it is indeed possible for 0 updates 
to be returned along with a new timestamp.

BUG=37373
TEST=manual testing of 2 browser sync; unit tests.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=42413

[tim (not reviewing), 2010-03-23 22:50:05]

I don't have any real comments besides the questions I asked offline, and one
suggestion below.

LGTM!

http://codereview.chromium.org/1161006/diff/2001/3005
File chrome/browser/sync/engine/process_updates_command.cc (right):

http://codereview.chromium.org/1161006/diff/2001/3005#newcode68
chrome/browser/sync/engine/process_updates_command.cc:68: // TODO(nick): The
following line makes no sense to me.
I think this was only ever for UI reporting, unlike the per-entry syncing bit
which is actually important. I think it was just so that if you're only doing a
GetUpdates (no commit) the UI would still show some throbber or something
implying that it's doing work... but yeah, doesn't make much sense.

http://codereview.chromium.org/1161006/diff/2001/3008
File chrome/browser/sync/engine/store_timestamps_command.h (right):

http://codereview.chromium.org/1161006/diff/2001/3008#newcode16
chrome/browser/sync/engine/store_timestamps_command.h:16: // ProcessUpdates.
nit - ProcessUpdatesCommand.

http://codereview.chromium.org/1161006/diff/2001/3017
File chrome/browser/sync/sessions/status_controller.h (right):

http://codereview.chromium.org/1161006/diff/2001/3017#newcode169
chrome/browser/sync/sessions/status_controller.h:169: bool
server_says_nothing_more_to_download() const {
it might be less subtle if you negate your has_new_timestamp check and call this
it server_says_more_to_download(), since the server has to actually "say"
something in that case. then the check in syncer.cc becomes
(!server_says_more_to_download()) APPLY_UPDATES