[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..94cba5f894b0c49f63bea3571a0a404d57877d46 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 +75,10 @@ class DataTypeController : public base::SupportsWeakPtr<DataTypeController> {
                               std::unique_ptr<base::ListValue>)>
       AllNodesCallback;
 
+  typedef base::Callback<void(syncer::ModelType,
+                              std::unique_ptr<syncer::StatusCounters>)>
+      StatusCountersCallback;
+
   typedef std::map<syncer::ModelType, std::unique_ptr<DataTypeController>>
       TypeMap;
   typedef std::map<syncer::ModelType, DataTypeController::State> StateMap;
@@ -151,6 +156,11 @@ 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 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);