IndexedDB: Have IDBCursor and IDBRequest explicitly break ref cycles

Source/modules/indexeddb/IDBCursor.cpp

Index: Source/modules/indexeddb/IDBCursor.cpp
diff --git a/Source/modules/indexeddb/IDBCursor.cpp b/Source/modules/indexeddb/IDBCursor.cpp
index bcf7bb7f74961946b5ece8b6f4a0db1d7f8034f4..68a346ca75a2dabf7ff02da0b1547b62853ca9c7 100644
--- a/Source/modules/indexeddb/IDBCursor.cpp
+++ b/Source/modules/indexeddb/IDBCursor.cpp
@@ -80,7 +80,6 @@ IDBCursor::IDBCursor(PassRefPtr<IDBCursorBackendInterface> backend, IndexedDB::C
     , m_direction(direction)
     , m_source(source)
     , m_transaction(transaction)
-    , m_transactionNotifier(transaction, this)
     , m_gotValue(false)
     , m_keyDirty(true)
     , m_primaryKeyDirty(true)
@@ -274,14 +273,23 @@ void IDBCursor::close()
 {
     // The notifier may be the last reference to this cursor.
     RefPtr<IDBCursor> protect(this);
-    m_transactionNotifier.cursorFinished();
-    if (m_request) {
-        m_request->finishCursor();
-        m_request.clear();
-    }
+    m_request.clear();
     m_backend.clear();
 }
 
+void IDBCursor::checkForReferenceCycle()
+{
+    // If this cursor and its request have the only references
+    // to each other, then explicitly break the cycle.
+    if (!m_request || m_request->getResultCursor() != this)
+        return;
+
+    if (!hasOneRef() || !m_request->hasOneRef())
+        return;
+
+    m_request.clear();
+}
+
 ScriptValue IDBCursor::key(ScriptExecutionContext* context)
 {
     m_keyDirty = false;