Invalidate :default pseudo classes when a default button is added or removed.

third_party/WebKit/Source/core/html/HTMLFormElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLFormElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLFormElement.cpp b/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
index 6519101a9743c6e73b791bb93a824e24b3032c94..1255c8d3c8ddcea5d4b088b7e65730d9e5313ff3 100644
--- a/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLFormElement.cpp
@@ -31,7 +31,6 @@
 #include "core/dom/Attribute.h"
 #include "core/dom/Document.h"
 #include "core/dom/ElementTraversal.h"
-#include "core/dom/IdTargetObserverRegistry.h"
 #include "core/dom/NodeListsNodeData.h"
 #include "core/events/AutocompleteErrorEvent.h"
 #include "core/events/Event.h"
@@ -71,6 +70,7 @@ HTMLFormElement::HTMLFormElement(Document& document)
     , m_associatedElementsAreDirty(false)
     , m_imageElementsAreDirty(false)
     , m_hasElementsAssociatedByParser(false)
+    , m_hasElementsAssociatedByFormAttribute(false)
     , m_didFinishParsingChildren(false)
     , m_wasUserSubmitted(false)
     , m_isSubmittingOrInUserJSSubmitEvent(false)
@@ -529,6 +529,8 @@ void HTMLFormElement::associate(FormAssociatedElement& e)
 {
     m_associatedElementsAreDirty = true;
     m_associatedElements.clear();
+    if (toHTMLElement(e).fastHasAttribute(formAttr))
+        m_hasElementsAssociatedByFormAttribute = true;
 }
 
 void HTMLFormElement::disassociate(FormAssociatedElement& e)
@@ -607,7 +609,7 @@ const FormAssociatedElement::List& HTMLFormElement::associatedElements() const
     Node* scope = mutableThis;
     if (m_hasElementsAssociatedByParser)
         scope = &NodeTraversal::highestAncestorOrSelf(*mutableThis);
-    if (inDocument() && treeScope().idTargetObserverRegistry().hasObservers(fastGetAttribute(idAttr)))
+    if (inDocument() && m_hasElementsAssociatedByFormAttribute)
         scope = &treeScope().rootNode();
     ASSERT(scope);
     collectAssociatedElements(*scope, mutableThis->m_associatedElements);
@@ -837,4 +839,14 @@ void HTMLFormElement::setDemoted(bool demoted)
     m_wasDemoted = demoted;
 }
 
+void HTMLFormElement::invalidateDefaultButtonStyle() const
+{
+    for (const auto& control : associatedElements()) {
+        if (!control->isFormControlElement())
+            return;

[rune, 2016/03/03 09:11:03]

Should this have been "continue;"?

[tkent, 2016/03/04 00:05:08]

Oops!  You're right.
I fixed it, and update the test so that it can catch this bug.

+        if (toHTMLFormControlElement(control)->canBeSuccessfulSubmitButton())
+            toHTMLFormControlElement(control)->pseudoStateChanged(CSSSelector::PseudoDefault);
+    }
+}
+
 } // namespace blink