Revert 243344 "IndexedDB: Fix cursor prefetching edge cases"

trunk/src/content/browser/indexed_db/indexed_db_cursor.cc

Index: trunk/src/content/browser/indexed_db/indexed_db_cursor.cc
===================================================================
--- trunk/src/content/browser/indexed_db/indexed_db_cursor.cc	(revision 243358)
+++ trunk/src/content/browser/indexed_db/indexed_db_cursor.cc	(working copy)
@@ -108,7 +108,8 @@
   std::vector<IndexedDBKey> found_primary_keys;
   std::vector<std::string> found_values;
 
-  saved_cursor_.reset();
+  if (cursor_)
+    saved_cursor_.reset(cursor_->Clone());
   const size_t max_size_estimate = 10 * 1024 * 1024;
   size_t size_estimate = 0;
 
@@ -118,12 +119,6 @@
       break;
     }
 
-    if (i == 0) {
-      // First prefetched result is always used, so that's the position
-      // a cursor should be reset to if the prefetch is invalidated.
-      saved_cursor_.reset(cursor_->Clone());
-    }
-
     found_keys.push_back(cursor_->key());
     found_primary_keys.push_back(cursor_->primary_key());
 
@@ -157,8 +152,7 @@
       found_keys, found_primary_keys, found_values);
 }
 
-void IndexedDBCursor::PrefetchReset(int used_prefetches,
-                                    int /* unused_prefetches */) {
+void IndexedDBCursor::PrefetchReset(int used_prefetches, int) {
   IDB_TRACE("IndexedDBCursor::PrefetchReset");
   cursor_.swap(saved_cursor_);
   saved_cursor_.reset();
@@ -166,9 +160,7 @@
   if (closed_)
     return;
   if (cursor_) {
-    // First prefetched result is always used.
-    DCHECK_GT(used_prefetches, 0);
-    for (int i = 0; i < used_prefetches - 1; ++i) {
+    for (int i = 0; i < used_prefetches; ++i) {
       bool ok = cursor_->Continue();
       DCHECK(ok);
     }