sync: don't notify from ~BaseTransaction if the writer is INVALID.

chrome/browser/sync/syncable/syncable.cc

Index: chrome/browser/sync/syncable/syncable.cc
diff --git a/chrome/browser/sync/syncable/syncable.cc b/chrome/browser/sync/syncable/syncable.cc
index efeecaf94440d8411742f63c28016e9bca6a3ec6..747e6bc2a5668947aafea4ef9faefd67b3835209 100644
--- a/chrome/browser/sync/syncable/syncable.cc
+++ b/chrome/browser/sync/syncable/syncable.cc
@@ -715,10 +715,12 @@ bool Directory::SaveChanges() {
 }
 
 void Directory::VacuumAfterSaveChanges(const SaveChangesSnapshot& snapshot) {
+  if (snapshot.dirty_metas.empty())
+    return;
+
   // Need a write transaction as we are about to permanently purge entries.
   WriteTransaction trans(FROM_HERE, VACUUM_AFTER_SAVE, this);
   ScopedKernelLock lock(this);
-  kernel_->flushed_metahandles.Push(0);  // Begin flush marker
   // Now drop everything we can out of memory.
   for (EntryKernelSet::const_iterator i = snapshot.dirty_metas.begin();
        i != snapshot.dirty_metas.end(); ++i) {
@@ -731,8 +733,6 @@ void Directory::VacuumAfterSaveChanges(const SaveChangesSnapshot& snapshot) {
       // We now drop deleted metahandles that are up to date on both the client
       // and the server.
       size_t num_erased = 0;
-      int64 handle = entry->ref(META_HANDLE);
-      kernel_->flushed_metahandles.Push(handle);
       num_erased = kernel_->ids_index->erase(entry);
       DCHECK_EQ(1u, num_erased);
       num_erased = kernel_->metahandles_index->erase(entry);
@@ -1158,8 +1158,10 @@ BaseTransaction::BaseTransaction(const tracked_objects::Location& from_here,
 }
 
 BaseTransaction::~BaseTransaction() {
-  dirkernel_->observers->Notify(
-      &TransactionObserver::OnTransactionEnd, from_here_, writer_);
+  if (writer_ != INVALID) {

[rlarocque, 2011/11/15 01:08:56]

What would happen if we removed this code altogether?  

The only clients of the TransactionObserver API are the sync JS classes.  I
glanced at that code and didn't see any use of "OnTransactionEnd" events, though
it's certainly possible that I missed something.  

The JS classes would still be notified of "OnTransactionWrite" events via
NotifyTransactionChangingAndEnding.  I think that's where most of the output in
the about:sync transaction log is generated.  

[rlarocque, 2011/11/15 01:23:06]

Never mind, I see how it's used now.  We use some JavaScript magic to register
for notifications of all sorts of event types.  

I'd still like to get rid of OnTransactionStart and OnTransactionEnd
notifications, but this CL is probably not he place to do it.  I withdraw my
comment.  

+    dirkernel_->observers->Notify(
+        &TransactionObserver::OnTransactionEnd, from_here_, writer_);
+  }
 }
 
 ReadTransaction::ReadTransaction(const tracked_objects::Location& location,