Use aggregate initialization for FlushJobInfo/CompactionJobInfo (#5997)

Summary:
FlushJobInfo and CompactionJobInfo are aggregates; we should use the
aggregate initialization syntax to ensure members (specifically those of
built-in types) are value-initialized.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5997

Test Plan: make check

Differential Revision: D18273398

Pulled By: ltamasi

fbshipit-source-id: 35b1a63ad9ca01605d288329858af72fffd7f392

db/compact_files_test.cc

@@ -387,7 +387,7 @@ TEST_F(CompactFilesTest, GetCompactionJobInfo) {
   auto l0_files_1 = collector->GetFlushedFiles();
   CompactionOptions co;
   co.compression = CompressionType::kLZ4Compression;
-  CompactionJobInfo compaction_job_info;
+  CompactionJobInfo compaction_job_info{};
   ASSERT_OK(
       db->CompactFiles(co, l0_files_1, 0, -1, nullptr, &compaction_job_info));
   ASSERT_EQ(compaction_job_info.base_input_level, 0);

db/db_impl/db_impl_compaction_flush.cc

@@ -570,7 +570,7 @@ void DBImpl::NotifyOnFlushBegin(ColumnFamilyData* cfd, FileMetaData* file_meta,
   // release lock while notifying events
   mutex_.Unlock();
   {
-    FlushJobInfo info;
+    FlushJobInfo info{};
     info.cf_id = cfd->GetID();
     info.cf_name = cfd->GetName();
     // TODO(yhchiang): make db_paths dynamic in case flush does not
@@ -1107,7 +1107,7 @@ void DBImpl::NotifyOnCompactionBegin(ColumnFamilyData* cfd, Compaction* c,
   mutex_.Unlock();
   TEST_SYNC_POINT("DBImpl::NotifyOnCompactionBegin::UnlockMutex");
   {
-    CompactionJobInfo info;
+    CompactionJobInfo info{};
     info.cf_name = cfd->GetName();
     info.status = st;
     info.thread_id = env_->GetThreadID();
@@ -1181,7 +1181,7 @@ void DBImpl::NotifyOnCompactionCompleted(
   mutex_.Unlock();
   TEST_SYNC_POINT("DBImpl::NotifyOnCompactionCompleted::UnlockMutex");
   {
-    CompactionJobInfo info;
+    CompactionJobInfo info{};
     BuildCompactionJobInfo(cfd, c, st, compaction_job_stats, job_id, current,
                            &info);
     for (auto listener : immutable_db_options_.listeners) {

db/flush_job.cc

@@ -431,7 +431,7 @@ Status FlushJob::WriteLevel0Table() {
 #ifndef ROCKSDB_LITE
 std::unique_ptr<FlushJobInfo> FlushJob::GetFlushJobInfo() const {
   db_mutex_->AssertHeld();
-  std::unique_ptr<FlushJobInfo> info(new FlushJobInfo);
+  std::unique_ptr<FlushJobInfo> info(new FlushJobInfo{});
   info->cf_id = cfd_->GetID();
   info->cf_name = cfd_->GetName();