Use container::back() and container::pop_back() for content.

content/child/indexed_db/webidbcursor_impl.cc

Index: content/child/indexed_db/webidbcursor_impl.cc
diff --git a/content/child/indexed_db/webidbcursor_impl.cc b/content/child/indexed_db/webidbcursor_impl.cc
index 946b08ddfc0dcd3d0c8d466e11f1171ed6f028c3..11294b688390ceab11b5412084c2ce9bf829687e 100644
--- a/content/child/indexed_db/webidbcursor_impl.cc
+++ b/content/child/indexed_db/webidbcursor_impl.cc
@@ -186,7 +186,7 @@ void WebIDBCursorImpl::ResetPrefetchCache() {
   continue_count_ = 0;
   prefetch_amount_ = kMinPrefetchAmount;
 
-  if (!prefetch_keys_.size()) {
+  if (prefetch_keys_.empty()) {
     // No prefetch cache, so no need to reset the cursor in the back-end.
     return;
   }