Count usage of reading HTMLInputElement::checked during click event handler.

Source/core/html/forms/BaseCheckableInputType.h

Index: Source/core/html/forms/BaseCheckableInputType.h
diff --git a/Source/core/html/forms/BaseCheckableInputType.h b/Source/core/html/forms/BaseCheckableInputType.h
index 27b10ba8157c26e5bfe06afc13557dc7c960c33f..f0f350654875030e2ac7f11c72f76b0f150250cc 100644
--- a/Source/core/html/forms/BaseCheckableInputType.h
+++ b/Source/core/html/forms/BaseCheckableInputType.h
@@ -38,9 +38,15 @@ namespace blink {
 // Base of checkbox and radio types.
 class BaseCheckableInputType : public InputType {
 protected:
-    BaseCheckableInputType(HTMLInputElement& element) : InputType(element) { }
+    BaseCheckableInputType(HTMLInputElement& element)
+        : InputType(element)
+        , m_isInClickHandler(false)
+    {
+    }
     void handleKeydownEvent(KeyboardEvent*) override;
 
+    bool m_isInClickHandler;
+
 private:
     FormControlState saveFormControlState() const final;
     void restoreFormControlState(const FormControlState&) final;
@@ -51,6 +57,7 @@ private:
     String fallbackValue() const final;
     bool storesValueSeparateFromAttribute() final;
     void setValue(const String&, bool, TextFieldEventBehavior) final;
+    void readingChecked() const final;
     bool isCheckable() final;
     bool shouldDispatchFormControlChangeEvent(String&, String&) override;
 };