[USS] Show USS counters in about:sync page

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 437c87301064129c1cd83939f3b280d8dc2b3913..2f7f45826f432136aeaebc12df77d926befc5928 100644
--- a/components/sync/driver/data_type_controller.h
+++ b/components/sync/driver/data_type_controller.h
@@ -16,6 +16,7 @@
 #include "components/sync/api/data_type_error_handler.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/base/unrecoverable_error_handler.h"
+#include "components/sync/engine/cycle/status_counters.h"
 
 namespace syncer {
 class SyncError;
@@ -74,6 +75,9 @@ class DataTypeController : public base::SupportsWeakPtr<DataTypeController> {
                               std::unique_ptr<base::ListValue>)>
       AllNodesCallback;
 
+  typedef base::Callback<void(syncer::ModelType, const syncer::StatusCounters&)>
+      StatusCountersCallback;
+
   typedef std::map<syncer::ModelType, std::unique_ptr<DataTypeController>>
       TypeMap;
   typedef std::map<syncer::ModelType, DataTypeController::State> StateMap;
@@ -151,6 +155,12 @@ class DataTypeController : public base::SupportsWeakPtr<DataTypeController> {
   // Used for populating nodes in Sync Node Browser of chrome://sync-internals.
   virtual void GetAllNodes(const AllNodesCallback& callback) = 0;
 
+  // Returns StatusCounters representing the counters for this data type to

[pavely, 2016/10/03 21:40:14]

Alternative for first sentence:
Collects StatusCounters for this datatype and passes them to |callback|.

[Gang Wu, 2016/10/06 00:20:22]

Done.

+  // |OnStatusCountersUpdated|, and |OnStatusCountersUpdated| will pass the
+  // StatusCounters through |callback|.
+  // Used for display counters in chrome://sync-internals.
+  virtual void GetStatusCounters(const StatusCountersCallback& callback) = 0;
+
  protected:
   DataTypeController(syncer::ModelType type, const base::Closure& dump_stack);