[SyncFS] Fix a bug in LevelDBWrapper::Iterator::Next

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper_unittest.cc

 // Copyright 2014 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 "chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.h"
 
 #include <string>
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
@@ skipping 97 matching lines @@
 
   itr->Next();
   EXPECT_TRUE(itr->Valid());
   EXPECT_EQ("d", itr->key().ToString());
   EXPECT_EQ("4", itr->value().ToString());
 
   itr->Next();
   EXPECT_FALSE(itr->Valid());
 }
 
+TEST_F(LevelDBWrapperTest, Iterator2Test) {
+  GetDB()->Put("a", "1");
+  GetDB()->Put("b", "2");
+  GetDB()->Put("c", "3");
+  // Keep pending transanctions on memory.
+
+  scoped_ptr<LevelDBWrapper::Iterator> itr = GetDB()->NewIterator();
+
+  std::string prev_key;
+  std::string prev_value;
+  int loop_counter = 0;
+  for (itr->SeekToFirst(); itr->Valid(); itr->Next()) {
+    ASSERT_NE(prev_key, itr->key().ToString());
+    ASSERT_NE(prev_value, itr->value().ToString());
+    prev_key = itr->key().ToString();
+    prev_value = itr->value().ToString();
+    ++loop_counter;
+  }
+  EXPECT_EQ(3, loop_counter);
+  EXPECT_EQ("c", prev_key);
+  EXPECT_EQ("3", prev_value);
+}
+
 TEST_F(LevelDBWrapperTest, PutTest) {
   TestData merged_data[] = {{"a", "1"}, {"aa", "new0"}, {"ab", "0"},
                             {"bb", "new2"}, {"c", "new1"}, {"d", "4"}};
   TestData orig_data[] = {{"a", "1"}, {"ab", "0"}, {"bb", "3"}, {"d", "4"}};
 
   CreateDefaultDatabase();
 
   // Add pending transactions.
   GetDB()->Put("aa", "new0");
   GetDB()->Put("c", "new1");
@@ skipping 50 matching lines @@
   GetDB()->Delete("ab");
   GetDB()->Commit();
   GetDB()->Clear();
 
   SCOPED_TRACE("DeleteTest_Commit");
   CheckDBContents(merged_data, arraysize(merged_data));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system