[Sync] Signal UIModelWorker to abort on sync shutdown.

components/sync/driver/glue/ui_model_worker.h

Index: components/sync/driver/glue/ui_model_worker.h
diff --git a/components/sync/driver/glue/ui_model_worker.h b/components/sync/driver/glue/ui_model_worker.h
index c3f76946a1fe0fa0b0e44eab19723e1bc047d1e0..8b8cfc8925ab6dd0134fd07655b9cb54257e011d 100644
--- a/components/sync/driver/glue/ui_model_worker.h
+++ b/components/sync/driver/glue/ui_model_worker.h
@@ -8,6 +8,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
+#include "base/synchronization/waitable_event.h"
 #include "components/sync/engine/model_safe_worker.h"
 
 namespace syncer {
@@ -17,9 +18,11 @@ namespace syncer {
 // from the MessageLoop home to the native model.
 class UIModelWorker : public ModelSafeWorker {
  public:
-  explicit UIModelWorker(scoped_refptr<base::SingleThreadTaskRunner> ui_thread);
+  explicit UIModelWorker(
+      const scoped_refptr<base::SingleThreadTaskRunner>& ui_thread);
 
-  // ModelSafeWorker implementation. Called on syncapi SyncerThread.
+  // ModelSafeWorker implementation.
+  void RequestStop() override;
   ModelSafeGroup GetModelSafeGroup() override;
   bool IsOnModelThread() override;
 
@@ -32,6 +35,10 @@ class UIModelWorker : public ModelSafeWorker {
   // A reference to the UI thread's task runner.
   const scoped_refptr<base::SingleThreadTaskRunner> ui_thread_;
 
+  // Signal set when work on native thread is done, aborted due to the thread
+  // being torn down, or aborted do to sync stopping.

[Nicolas Zea, 2016/11/10 22:27:07]

typo: do -> due

[Nicolas Zea, 2016/11/10 22:27:07]

nit: i think it's worth explaining why we need this (namely that the UI thread
can join on the sync thread, and this prevents the sync thread from waiting on
work on the UI thread)

[maxbogue, 2016/11/12 03:19:52]

Done.

[maxbogue, 2016/11/12 03:19:52]

Done.

+  base::WaitableEvent work_done_or_abandoned_;
+
   DISALLOW_COPY_AND_ASSIGN(UIModelWorker);
 };