Non-activated default buttons prevent implicit form submission.

Source/core/html/HTMLFormControlElement.cpp

Index: Source/core/html/HTMLFormControlElement.cpp
diff --git a/Source/core/html/HTMLFormControlElement.cpp b/Source/core/html/HTMLFormControlElement.cpp
index e3c52907a668e751fff8cea93f78764b3a88191a..1cb8c3b46f222881b1e53e2512c6e8c10d431f5a 100644
--- a/Source/core/html/HTMLFormControlElement.cpp
+++ b/Source/core/html/HTMLFormControlElement.cpp
@@ -503,6 +503,13 @@ HTMLFormElement* HTMLFormControlElement::virtualForm() const
     return FormAssociatedElement::form();
 }
 
+bool HTMLFormControlElement::isSuccessfulSubmitButton() const
+{
+    // HTML spec says that buttons must have names to be considered successful.
+    // However, other browsers do not impose this constraint. So we do not.
+    return canBeSuccessfulSubmitButton() && !isDisabledFormControl();
+}
+
 bool HTMLFormControlElement::isDefaultButtonForForm() const
 {
     return isSuccessfulSubmitButton() && form() && form()->defaultButton() == this;