Add UMA for popup overlays removed from saved MHTML page

third_party/WebKit/Source/core/frame/FrameSerializer.h

Index: third_party/WebKit/Source/core/frame/FrameSerializer.h
diff --git a/third_party/WebKit/Source/core/frame/FrameSerializer.h b/third_party/WebKit/Source/core/frame/FrameSerializer.h
index ff8c650017298e501b6477da687d298825f4ff80..b53d02d984a0f7defee3763e8f5217ef5ff9e5fd 100644
--- a/third_party/WebKit/Source/core/frame/FrameSerializer.h
+++ b/third_party/WebKit/Source/core/frame/FrameSerializer.h
@@ -70,6 +70,8 @@ class CORE_EXPORT FrameSerializer final {
 
   class Delegate {
    public:
+    virtual ~Delegate() {}
+
     // Controls whether HTML serialization should skip the given element.
     virtual bool ShouldIgnoreElement(const Element&) { return false; }