Make PaintImages a class and implement a Clone() method.

third_party/WebKit/Source/core/style/PaintImages.h

Index: third_party/WebKit/Source/core/style/PaintImages.h
diff --git a/third_party/WebKit/Source/core/style/PaintImages.h b/third_party/WebKit/Source/core/style/PaintImages.h
new file mode 100644
index 0000000000000000000000000000000000000000..27864fedab6ce66736d6c89119438b39de3ad4a8
--- /dev/null
+++ b/third_party/WebKit/Source/core/style/PaintImages.h
@@ -0,0 +1,26 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PaintImages_h
+#define PaintImages_h
+
+#include <memory>
+#include "core/style/StyleImage.h"
+#include "platform/heap/Persistent.h"
+#include "platform/wtf/PtrUtil.h"
+#include "platform/wtf/Vector.h"
+
+namespace blink {
+
+// Not to be deleted through a pointer to the base class.
+class PaintImages : public Vector<Persistent<StyleImage>> {
+ public:
+  std::unique_ptr<PaintImages> Clone() const {
+    return WTF::WrapUnique(new PaintImages(*this));
+  }
+};
+
+}  // namespace blink
+
+#endif  // PaintImages_h