Persist Directory to disk when the app is backgrounded.

chrome/browser/sync/glue/sync_backend_host_impl.cc

Index: chrome/browser/sync/glue/sync_backend_host_impl.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host_impl.cc b/chrome/browser/sync/glue/sync_backend_host_impl.cc
index 6f4c7e37ddf33d03afb5f97c658ece1ab55ab2c4..e414b37ebcf2eed9019a1a8961b42de04547c4b2 100644
--- a/chrome/browser/sync/glue/sync_backend_host_impl.cc
+++ b/chrome/browser/sync/glue/sync_backend_host_impl.cc
@@ -33,6 +33,7 @@
 #include "sync/internal_api/public/sync_manager_factory.h"
 #include "sync/internal_api/public/util/experiments.h"
 #include "sync/internal_api/public/util/sync_string_conversions.h"
+#include "sync/syncable/directory.h"
 
 // Helper macros to log with the syncer thread name; useful when there
 // are multiple syncers involved.
@@ -520,6 +521,18 @@ SyncedDeviceTracker* SyncBackendHostImpl::GetSyncedDeviceTracker() const {
   return core_->synced_device_tracker();
 }
 
+void FlushDirectoryWrapper(syncer::syncable::Directory* directory) {

[maniscalco, 2014/09/10 17:49:03]

What's the motivation for using this free function in the Bind instead of
binding to Directory::SaveChanges?

[maxbogue, 2014/09/10 20:11:01]

Directory::SaveChanges returns a bool, so it cannot be used as a Closure. Added
a comment saying so.

[maniscalco, 2014/09/10 20:19:25]

Ah, check out IgnoreResult:

https://code.google.com/p/chromium/codesearch#chromium/src/base/callback.h&l=167

That should let you forego the extra free function.

[maxbogue, 2014/09/12 16:45:38]

Done.

+  directory->SaveChanges();
+}
+
+void SyncBackendHostImpl::FlushDirectory() const {

[nyquist, 2014/09/10 17:43:09]

Does this require the sync engine to be initialized?

[maxbogue, 2014/09/10 20:11:01]

I kind of assumed that directory being NULL meant sync was uninitialized,
meaning this function can be called but does nothing if it's not initialized.
Nicholas, is that correct?

+  syncer::syncable::Directory* directory = GetUserShare()->directory.get();
+  if (directory != nullptr) {

[nyquist, 2014/09/10 17:43:09]

!= NULL ?

[maxbogue, 2014/09/10 20:11:01]

Done.

+    registrar_->sync_thread()->message_loop()->PostTask(FROM_HERE,
+        base::Bind(&FlushDirectoryWrapper, directory));

[maniscalco, 2014/09/10 20:19:25]

As we talked about in person over lunch, it seems like the tricky part is
ensuring that when the task eventually executes in the sync thread, the
directory is still around.  It seems like we could end up calling SaveChanges on
a deleted Directory.  Maybe zea@ has some suggestions here?

[maxbogue, 2014/09/12 16:45:38]

Routed through SyncBackendHostCore to try to solve this problem.

+  }
+}
+
 void SyncBackendHostImpl::RequestBufferedProtocolEventsAndEnableForwarding() {
   registrar_->sync_thread()->message_loop()->PostTask(
       FROM_HERE,