Add Autofill preview support for <select> input fields

Source/core/html/HTMLSelectElement.h

Index: Source/core/html/HTMLSelectElement.h
diff --git a/Source/core/html/HTMLSelectElement.h b/Source/core/html/HTMLSelectElement.h
index ebb30b4b184ddccb1890f1222ef669051eff4737..f25250843c573133cd6e1f01d700463cc809028a 100644
--- a/Source/core/html/HTMLSelectElement.h
+++ b/Source/core/html/HTMLSelectElement.h
@@ -68,6 +68,10 @@ public:
 
     String value() const;
     void setValue(const String&);
+    String suggestedValue() const;
+    void setSuggestedValue(const String&);
+    String originalValue() const;
+    void setOriginalValue(const String&);
 
     PassRefPtr<HTMLOptionsCollection> options();
     PassRefPtr<HTMLCollection> selectedOptions();
@@ -208,6 +212,8 @@ private:
     bool m_activeSelectionState;
     mutable bool m_shouldRecalcListItems;
     bool m_isParsingInProgress;
+    String m_suggestedValue;
+    String m_originalValue;
 };
 
 DEFINE_NODE_TYPE_CASTS(HTMLSelectElement, hasTagName(HTMLNames::selectTag));