[SyncFS] Support Delete operation on LevelDBWrapper::Iterator

After running Delete() method, the iterator is expected to index
the next entry, if exists.


BUG=347425
TEST=./unit_tests --gtest_filter="LevelDBWrapper*"

Review URL: https://codereview.chromium.org/461823002

Cr-Commit-Position: refs/heads/master@{#288991}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288991 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc

@@ -67,6 +67,20 @@ void LevelDBWrapper::Iterator::Next() {
   AdvanceIterators();
 }
 
+void LevelDBWrapper::Iterator::Delete() {
+  DCHECK(Valid());
+
+  const std::string key_str = key().ToString();
+  Transaction deletion(DELETE_OPERATION, std::string());
+  map_iterator_ = db_->pending_.insert(map_iterator_,
+                                       std::make_pair(key_str, deletion));
+  // In case that |db_->pending_| already had an entry for the key, we have to
+  // update the value.
+  map_iterator_->second = deletion;
+
+  AdvanceIterators();
+}
+
 leveldb::Slice LevelDBWrapper::Iterator::key() {
   DCHECK(Valid());
 

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.h

@@ -56,6 +56,7 @@ class LevelDBWrapper {
     void SeekToFirst();
     void SeekToLast();
     void Next();
+    void Delete();
     leveldb::Slice key();
     leveldb::Slice value();
 

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper_unittest.cc

@@ -113,6 +113,21 @@ TEST_F(LevelDBWrapperTest, IteratorTest) {
 
   itr->Next();
   EXPECT_FALSE(itr->Valid());
+
+  itr->SeekToFirst();
+  EXPECT_TRUE(itr->Valid());
+  EXPECT_EQ("a", itr->key().ToString());
+  EXPECT_EQ("1", itr->value().ToString());
+
+  itr->Delete();
+  EXPECT_TRUE(itr->Valid());
+  EXPECT_EQ("ab", itr->key().ToString());
+  EXPECT_EQ("0", itr->value().ToString());
+
+  itr->SeekToFirst();
+  EXPECT_TRUE(itr->Valid());
+  EXPECT_EQ("ab", itr->key().ToString());
+  EXPECT_EQ("0", itr->value().ToString());
 }
 
 TEST_F(LevelDBWrapperTest, Iterator2Test) {