Add non-blocking sync code to ProfileSyncService

chrome/browser/sync/glue/sync_backend_host_core.cc

Index: chrome/browser/sync/glue/sync_backend_host_core.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host_core.cc b/chrome/browser/sync/glue/sync_backend_host_core.cc
index c433b0b3df96046427e6e0d2d94c0245df866300..d1ac1068bb4051783908322c420f6942d9643dc0 100644
--- a/chrome/browser/sync/glue/sync_backend_host_core.cc
+++ b/chrome/browser/sync/glue/sync_backend_host_core.cc
@@ -473,16 +473,26 @@ void SyncBackendHostCore::DoInitialProcessControlTypes() {
 }
 
 void SyncBackendHostCore::DoFinishInitialProcessControlTypes() {
+  DCHECK_EQ(base::MessageLoop::current(), sync_loop_);
+
   registrar_->ActivateDataType(syncer::DEVICE_INFO,
                                syncer::GROUP_PASSIVE,
                                synced_device_tracker_.get(),
                                sync_manager_->GetUserShare());
 
+  base::WeakPtr<syncer::SyncCore> sync_core = sync_manager_->GetSyncCore();
+
+  // De-reference the WeakPtr while we're here to signal to the debugging
+  // mechanisms that it belongs to the sync thread.  This helps us DCHECK
+  // earlier if the pointer is misused.
+  sync_core.get();

[Nicolas Zea, 2014/04/02 23:19:05]

I don't think this is necessary. A weak pointer always belongs to the thread it
was created on (see the constructor for SequenceCheckerImpl). It's only verified
when IsValid is checked, but the ownership is assigned at construction time.

[rlarocque, 2014/04/03 01:03:46]

IIRC, I added this statement because it helped me debug a crash, then decided to
leave it in since it was helpful.

The WeakReference::Flag constructor calls DetachFromSequence() on its
SequenceChecker.  Wouldn't that undo the association created in the
SequenceChecker's construction?

[Nicolas Zea, 2014/04/03 17:52:15]

Huh, I missed that. Fair enough then.

+
   host_.Call(
       FROM_HERE,
       &SyncBackendHostImpl::HandleInitializationSuccessOnFrontendLoop,
       js_backend_,
-      debug_info_listener_);
+      debug_info_listener_,
+      sync_core);
 
   js_backend_.Reset();
   debug_info_listener_.Reset();