sync: Move unique_client_tag hashing code

sync/syncable/syncable_util.cc

Index: sync/syncable/syncable_util.cc
diff --git a/sync/syncable/syncable_util.cc b/sync/syncable/syncable_util.cc
index 36d08d0146f6d6c175edb2732a93e4d4ede80a8e..0597109d41b62426c822fd40fce51904d35b69b3 100644
--- a/sync/syncable/syncable_util.cc
+++ b/sync/syncable/syncable_util.cc
@@ -4,8 +4,10 @@
 
 #include "sync/syncable/syncable_util.h"
 
+#include "base/base64.h"
 #include "base/location.h"
 #include "base/logging.h"
+#include "base/sha1.h"
 #include "sync/syncable/directory.h"
 #include "sync/syncable/entry.h"
 #include "sync/syncable/mutable_entry.h"
@@ -102,5 +104,20 @@ bool SyncAssert(bool condition,
   return true;
 }
 
+std::string GenerateSyncableHash(
+    ModelType model_type, const std::string& client_tag) {
+  // Blank PB with just the field in it has termination symbol,
+  // handy for delimiter.
+  sync_pb::EntitySpecifics serialized_type;
+  AddDefaultFieldValue(model_type, &serialized_type);
+  std::string hash_input;
+  serialized_type.AppendToString(&hash_input);
+  hash_input.append(client_tag);
+
+  std::string encode_output;
+  CHECK(base::Base64Encode(base::SHA1HashString(hash_input), &encode_output));
+  return encode_output;
+}
+
 }  // namespace syncable
 }  // namespace syncer