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

content/browser/indexed_db/leveldb/leveldb_iterator.h

Index: content/browser/indexed_db/leveldb/leveldb_iterator.h
diff --git a/content/browser/indexed_db/leveldb/leveldb_iterator.h b/content/browser/indexed_db/leveldb/leveldb_iterator.h
index d5efa4bf51951f6218d0cbcb804e282c6397b4d2..ce56ab9a5eea3cc336ecc764c701602d2616f677 100644
--- a/content/browser/indexed_db/leveldb/leveldb_iterator.h
+++ b/content/browser/indexed_db/leveldb/leveldb_iterator.h
@@ -21,6 +21,12 @@ class CONTENT_EXPORT LevelDBIterator {
   virtual leveldb::Status Prev() = 0;
   virtual base::StringPiece Key() const = 0;
   virtual base::StringPiece Value() const = 0;
+
+  // Detaches the internal iterator which saves memory at the performance
+  // expense of reloading and seeking later if the iterator is needed again for
+  // |Seek*|, |Next|, |Prev|, or |Value|.
+  virtual void Detach(){};

[jsbell, 2017/03/27 15:35:34]

Nit: space between ) and {

Also, since we DCHECK if you call Detach() twice in the impl that should be
noted as part of the contract.

[dmurph, 2017/03/27 21:32:05]

ugh. Darn clang format! Actually, should I just keep it this way because it's
clang-formatted? It keeps reverting every time I run git cl format.

[pwnall, 2017/03/27 21:52:18]

I would suggest keeping the code as-is and and filing a bug.

+  virtual bool IsDetached() const;
 };
 
 }  // namespace content