[USS] Move GetAllNodes from backend to controller

components/sync/driver/data_type_controller.h

Index: components/sync/driver/data_type_controller.h
diff --git a/components/sync/driver/data_type_controller.h b/components/sync/driver/data_type_controller.h
index 7035b5dcb78b8dc994a0c4529f7368b64a008558..b1414b3c62812190ad84b6eb4ceb93ea6453eab4 100644
--- a/components/sync/driver/data_type_controller.h
+++ b/components/sync/driver/data_type_controller.h
@@ -12,6 +12,7 @@
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/ref_counted_delete_on_message_loop.h"
+#include "base/memory/scoped_vector.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/base/unrecoverable_error_handler.h"
@@ -75,6 +76,9 @@ class DataTypeController
 
   typedef base::Callback<void(syncer::ModelType, syncer::SyncError)>
       ModelLoadCallback;
+  typedef base::Callback<void(const std::vector<syncer::ModelType>& type,

[maxbogue, 2016/08/25 23:38:59]

It would make more sense if the callback was just for the one type:

base::Callback<syncer::ModelType, std::unique_ptr<base::ListValue>>

[Gang Wu, 2016/08/26 16:48:04]

Done.

+                              ScopedVector<base::ListValue>)>
+      AllNodesCallback;
 
   typedef std::map<syncer::ModelType, scoped_refptr<DataTypeController>>
       TypeMap;
@@ -153,6 +157,9 @@ class DataTypeController
   // Returns true by default.
   virtual bool ReadyForStart() const;
 
+  virtual void GetAllNodes(scoped_refptr<base::SequencedTaskRunner> task_runner,

[maxbogue, 2016/08/25 23:38:59]

You don't need the task runner here, either. This is always going to be done on
the UI thread and if the DTC is going to thread hop away, it can always grab the
UI thread handle itself.

[Gang Wu, 2016/08/26 16:48:04]

Done.

+                           const AllNodesCallback& callback) = 0;
+
  protected:
   friend class base::RefCountedDeleteOnMessageLoop<DataTypeController>;
   friend class base::DeleteHelper<DataTypeController>;