[Sync] Handle invalid specifics field numbers gracefully

sync/syncable/model_type_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/internal_api/public/base/model_type.h"
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/test/values_test_util.h"
@@ skipping 52 matching lines @@
 
 TEST_F(ModelTypeTest, IsRealDataType) {
   EXPECT_FALSE(IsRealDataType(UNSPECIFIED));
   EXPECT_FALSE(IsRealDataType(MODEL_TYPE_COUNT));
   EXPECT_FALSE(IsRealDataType(TOP_LEVEL_FOLDER));
   EXPECT_TRUE(IsRealDataType(FIRST_REAL_MODEL_TYPE));
   EXPECT_TRUE(IsRealDataType(BOOKMARKS));
   EXPECT_TRUE(IsRealDataType(APPS));
 }
 
+// Make sure we can convert ModelTypes to and from specifics field
+// numbers.
+TEST_F(ModelTypeTest, ModelTypeToFromSpecificsFieldNumber) {
+  for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; ++i) {
+    ModelType model_type = ModelTypeFromInt(i);
+    int field_number = GetSpecificsFieldNumberFromModelType(model_type);
+    EXPECT_EQ(model_type,
+              GetModelTypeFromSpecificsFieldNumber(field_number));
+  }
+}
+
+TEST_F(ModelTypeTest, ModelTypeOfInvalidSpecificsFieldNumber) {
+  EXPECT_EQ(UNSPECIFIED, GetModelTypeFromSpecificsFieldNumber(0));
+}
+
 }  // namespace
 }  // namespace syncer