IndexedDB: Added UMA stat to measure time to close backing store.

content/browser/indexed_db/leveldb/leveldb_database.cc

Index: content/browser/indexed_db/leveldb/leveldb_database.cc
diff --git a/content/browser/indexed_db/leveldb/leveldb_database.cc b/content/browser/indexed_db/leveldb/leveldb_database.cc
index 459a16e473a529d083775ca368415855572a5a34..2c18f1f5170f34448b4d01f43f28bb82913ed6ab 100644
--- a/content/browser/indexed_db/leveldb/leveldb_database.cc
+++ b/content/browser/indexed_db/leveldb/leveldb_database.cc
@@ -86,11 +86,20 @@ LevelDBDatabase::LevelDBDatabase() {}
 
 LevelDBDatabase::~LevelDBDatabase() {

[dgrogan, 2015/06/18 22:15:58]

Mainly for my edification:

Looks like this gets called when the ref count on an instance of
IndexedDBBackingStore drops to 0, is that right? Is there still a timer that
keeps the database open for 2 seconds?

[cmumford, 2015/06/18 22:20:14]

Yes, timer is still in IndexedDBFactoryImpl::ReleaseBackingStore(). So when the
timer closes the backing store (and eventually the LevelDBDatabase) this
function will be executed.

   // db_'s destructor uses comparator_adapter_; order of deletion is important.
-  db_.reset();
+  CloseDatabase();
   comparator_adapter_.reset();
   env_.reset();
 }
 
+void LevelDBDatabase::CloseDatabase() {
+  if (db_) {
+    base::TimeTicks begin_time = base::TimeTicks::Now();
+    db_.reset();
+    UMA_HISTOGRAM_MEDIUM_TIMES("WebCore.IndexedDB.LevelDB.CloseTime",
+                               base::TimeTicks::Now() - begin_time);
+  }
+}
+
 static leveldb::Status OpenDB(
     leveldb::Comparator* comparator,
     leveldb::Env* env,