[IndexedDB] Pool and evict leveldb iterators, to save memory

content/browser/indexed_db/indexed_db_backing_store.cc

Index: content/browser/indexed_db/indexed_db_backing_store.cc
diff --git a/content/browser/indexed_db/indexed_db_backing_store.cc b/content/browser/indexed_db/indexed_db_backing_store.cc
index ffb0f8fc5f69577c84d32e8805a742aa6649faf5..00e22b7700f28fe2e6c1ec2bb86e64854110f615 100644
--- a/content/browser/indexed_db/indexed_db_backing_store.cc
+++ b/content/browser/indexed_db/indexed_db_backing_store.cc
@@ -58,6 +58,7 @@ using url::Origin;
 namespace content {
 
 namespace {
+static const size_t kDefaultMaxOpenIteratorsPerDatabase = 50;
 
 enum IndexedDBBackingStoreErrorSource {
   // 0 - 2 are no longer used.
@@ -1064,7 +1065,9 @@ class DefaultLevelDBFactory : public LevelDBFactory {
                      const LevelDBComparator* comparator,
                      std::unique_ptr<LevelDBDatabase>* db,
                      bool* is_disk_full) override {
-    return LevelDBDatabase::Open(file_name, comparator, db, is_disk_full);
+    return LevelDBDatabase::Open(file_name, comparator, db,
+                                 kDefaultMaxOpenIteratorsPerDatabase,
+                                 is_disk_full);
   }
   Status DestroyLevelDB(const FilePath& file_name) override {
     return LevelDBDatabase::Destroy(file_name);