Bug 591737 - Add pref for details and summary elements. r=bz

dom/html/HTMLDetailsElement.cpp

@@ -6,12 +6,39 @@
 #include "mozilla/dom/HTMLDetailsElement.h"
 
 #include "mozilla/dom/HTMLDetailsElementBinding.h"
+#include "mozilla/dom/HTMLUnknownElement.h"
+#include "mozilla/Preferences.h"
 
-NS_IMPL_NS_NEW_HTML_ELEMENT(Details)
+// Expand NS_IMPL_NS_NEW_HTML_ELEMENT(Details) to add pref check.
+nsGenericHTMLElement*
+NS_NewHTMLDetailsElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
+                         mozilla::dom::FromParser aFromParser)
+{
+  if (!mozilla::dom::HTMLDetailsElement::IsDetailsEnabled()) {
+    return new mozilla::dom::HTMLUnknownElement(aNodeInfo);
+  }
+
+  return new mozilla::dom::HTMLDetailsElement(aNodeInfo);
+}
 
 namespace mozilla {
 namespace dom {
 
+bool
+HTMLDetailsElement::IsDetailsEnabled()
+{
+  static bool isDetailsEnabled = false;
+  static bool added = false;
+
+  if (!added) {
+    Preferences::AddBoolVarCache(&isDetailsEnabled,
+                                 "dom.details_element.enabled");
+    added = true;
+  }
+
+  return isDetailsEnabled;
+}
+
 HTMLDetailsElement::~HTMLDetailsElement()
 {
 }