Escape all of invalid values in console messages for INPUT elements.

Source/platform/JSONValues.h

Index: Source/platform/JSONValues.h
diff --git a/Source/platform/JSONValues.h b/Source/platform/JSONValues.h
index 41ebca9fc8592f1a78790e2fb6fec28bdb841b6d..73b19c39ffbbbb994f75c626176fbfdd4be2abeb 100644
--- a/Source/platform/JSONValues.h
+++ b/Source/platform/JSONValues.h
@@ -117,6 +117,8 @@ public:
     virtual void writeJSON(StringBuilder* output) const;
     virtual void prettyWriteJSON(StringBuilder* output) const;
 
+    static String quoteString(const String&);
+
 protected:
     explicit JSONValue(Type type) : m_type(type) { }
     virtual void prettyWriteJSONInternal(StringBuilder* output, int depth) const;