1 files changed, 5 insertions, 1 deletions
diff --git a/chromium/third_party/WebKit/Source/core/dom/QualifiedName.cpp b/chromium/third_party/WebKit/Source/core/dom/QualifiedName.cpp
index 8a17372a4ca..32acc2a87a8 100644
--- a/chromium/third_party/WebKit/Source/core/dom/QualifiedName.cpp
+++ b/chromium/third_party/WebKit/Source/core/dom/QualifiedName.cpp
@@ -106,9 +106,13 @@ QualifiedName::QualifiedNameImpl::~QualifiedNameImpl() {
 }
 
 String QualifiedName::ToString() const {
-  String local = LocalName();
+  const String& local = LocalName().GetString();
   if (HasPrefix())
     return Prefix().GetString() + ":" + local;
+#if !defined(NDEBUG)
+  if (!local.IsSafeToSendToAnotherThread())
+      return local.IsolatedCopy();
+#endif
   return local;
 }