Sync: Support multiple setup UIs.

components/browser_sync/browser/profile_sync_service.cc

Index: components/browser_sync/browser/profile_sync_service.cc
diff --git a/components/browser_sync/browser/profile_sync_service.cc b/components/browser_sync/browser/profile_sync_service.cc
index a41b846d748d38185b63c7bdc93751727ff758ed..66489bf320f0c3c638dfe0beaafb8e445c0454f3 100644
--- a/components/browser_sync/browser/profile_sync_service.cc
+++ b/components/browser_sync/browser/profile_sync_service.cc
@@ -1530,15 +1530,18 @@ bool ProfileSyncService::IsFirstSetupInProgress() const {
   return !IsFirstSetupComplete() && startup_controller_->IsSetupInProgress();
 }
 
-void ProfileSyncService::SetSetupInProgress(bool setup_in_progress) {
-  // This method is a no-op if |setup_in_progress_| remains unchanged.
-  if (startup_controller_->IsSetupInProgress() == setup_in_progress)
-    return;
+std::unique_ptr<sync_driver::SyncSetupInProgressHandle>
+ProfileSyncService::GetSetupInProgressHandle() {
+  if (++outstanding_setup_in_progress_handles_ == 1 &&
+      !startup_controller_->IsSetupInProgress()) {

[maxbogue, 2016/06/10 17:28:46]

You could probably DCHECK the !IsSetupInProgress part, no? Would be bad if the
count was 0 and that was true.

[tommycli, 2016/06/10 18:58:21]

Done. You're right that would really surprise me.

+    startup_controller_->SetSetupInProgress(true);
+    NotifyObservers();
+  }
 
-  startup_controller_->SetSetupInProgress(setup_in_progress);
-  if (!setup_in_progress && IsBackendInitialized())
-    ReconfigureDatatypeManager();
-  NotifyObservers();
+  return std::unique_ptr<sync_driver::SyncSetupInProgressHandle>(
+      new sync_driver::SyncSetupInProgressHandle(
+          base::Bind(&ProfileSyncService::OnSetupInProgressHandleDestroyed,
+                     weak_factory_.GetWeakPtr())));
 }
 
 bool ProfileSyncService::IsSyncAllowed() const {
@@ -2544,3 +2547,17 @@ tracked_objects::Location ProfileSyncService::unrecoverable_error_location()
     const {
   return unrecoverable_error_location_;
 }
+
+void ProfileSyncService::OnSetupInProgressHandleDestroyed() {
+  // Don't re-start Sync until all outstanding handles are destroyed.
+  if (--outstanding_setup_in_progress_handles_ != 0)
+    return;
+
+  if (!startup_controller_->IsSetupInProgress())

[maxbogue, 2016/06/10 17:28:46]

Same as above, would it make sense to DCHECK instead?

[tommycli, 2016/06/10 18:58:20]

Done.

+    return;
+
+  startup_controller_->SetSetupInProgress(false);
+  if (IsBackendInitialized())
+    ReconfigureDatatypeManager();
+  NotifyObservers();
+}