Fix status counters in chrome://sync-internals

The regression was introduced in
https://chromium-review.googlesource.com/1160229 which overlooked the
fact that the UI makes assumptions about when it's notified about the
results (i.e. no synchronous reply expected).

There are cleaner alternatives to the proposed fix, but it seems most
conservative to go back to the previous implementation by partially
reverting the offending patch.

Bug: None
Change-Id: I81d82d27234666d407708b1ccd366e493784e9c5
Reviewed-on: https://chromium-review.googlesource.com/1169045
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581880}

components/browser_sync/profile_sync_service.cc

@@ -26,6 +26,7 @@
 #include "components/signin/core/browser/account_info.h"
 #include "components/signin/core/browser/signin_manager.h"
 #include "components/signin/core/browser/signin_metrics.h"
+#include "components/sync/base/bind_to_task_runner.h"
 #include "components/sync/base/cryptographer.h"
 #include "components/sync/base/passphrase_type.h"
 #include "components/sync/base/report_unrecoverable_error.h"
@@ -1714,9 +1715,13 @@ std::unique_ptr<base::Value> ProfileSyncService::GetTypeStatusMap() {
                                           dtc_iter->second->state()));
       if (dtc_iter->second->state() !=
           syncer::DataTypeController::NOT_RUNNING) {
-        dtc_iter->second->GetStatusCounters(base::BindRepeating(
-            &ProfileSyncService::OnDatatypeStatusCounterUpdated,
-            base::Unretained(this)));
+        // We use BindToCurrentSequence() to make sure observers (i.e.
+        // |type_debug_info_observers_|) are not notified synchronously, which
+        // the UI code (chrome://sync-internals) doesn't handle well.
+        dtc_iter->second->GetStatusCounters(
+            BindToCurrentSequence(base::BindRepeating(
+                &ProfileSyncService::OnDatatypeStatusCounterUpdated,
+                base::Unretained(this))));
       }
     }