Dispatch change event for input type=checkbox when checked but value is null

Source/core/html/forms/CheckboxInputType.cpp

Index: Source/core/html/forms/CheckboxInputType.cpp
diff --git a/Source/core/html/forms/CheckboxInputType.cpp b/Source/core/html/forms/CheckboxInputType.cpp
index 738f9d58b9b0b15abb71a562058d9f40f5284f47..d2d803f9471cf4365a02f2110d65f7b9d8859d97 100644
--- a/Source/core/html/forms/CheckboxInputType.cpp
+++ b/Source/core/html/forms/CheckboxInputType.cpp
@@ -107,4 +107,9 @@ bool CheckboxInputType::supportsIndeterminateAppearance() const
     return true;
 }
 
+bool CheckboxInputType::shouldDispatchFormControlChangeEvent(String& oldValue, String& newValue)
+{
+    return oldValue != newValue;
+}
+
 } // namespace WebCore