[Sync] Renaming client key to client tag.

sync/api/data_batch.h

Index: sync/api/data_batch.h
diff --git a/sync/api/data_batch.h b/sync/api/data_batch.h
index 68d68e015607cc0fffd7e732b750725df7aa5da8..d7e769baf15c01b2b34e5f9cd06fcfec8f449366 100644
--- a/sync/api/data_batch.h
+++ b/sync/api/data_batch.h
@@ -15,7 +15,7 @@
 
 namespace syncer_v2 {
 
-typedef std::pair<std::string, scoped_ptr<EntityData>> KeyAndData;
+typedef std::pair<std::string, scoped_ptr<EntityData>> TagAndData;
 
 // Interface used by the processor to read data requested from the service.
 class SYNC_EXPORT DataBatch {
@@ -26,10 +26,10 @@ class SYNC_EXPORT DataBatch {
   // Returns if the data batch has another pair or not.
   virtual bool HasNext() const = 0;
 
-  // Returns a pair of storage key and owned entity data object. Invoking this
+  // Returns a pair of storage tag and owned entity data object. Invoking this
   // method will remove the pair from the batch, and should not be called if
   // HasNext() returns false.
-  virtual KeyAndData Next() = 0;
+  virtual TagAndData Next() = 0;
 };
 
 }  // namespace syncer_v2