Fix race condition that causes valgrind failures

Summary: DBTest.DynamicLevelCompressionPerLevel2 sometimes fails during valgrind runs.  This causes our valgrind tests to fail.  Not sure what the best fix is for this test, but hopefully this simple change is sufficient.

Test Plan: run test

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D51111

db/db_test.cc

@@ -7466,8 +7466,14 @@ TEST_F(DBTest, DynamicLevelCompressionPerLevel2) {
 
   for (int i = 0; i < 100; i++) {
     ASSERT_OK(Put(Key(keys[i]), RandomString(&rnd, 200)));
+
+    if (i % 25 == 0) {
+      dbfull()->TEST_WaitForFlushMemTable();
+    }
   }
+
   Flush();
+  dbfull()->TEST_WaitForFlushMemTable();
   dbfull()->TEST_WaitForCompact();
   rocksdb::SyncPoint::GetInstance()->DisableProcessing();
   rocksdb::SyncPoint::GetInstance()->ClearAllCallBacks();