Back out bug 1031945 for now because we have silly pref settings on mobile and dumb tests. a=orange

dom/base/nsGlobalWindow.cpp

@@ -4365,21 +4365,6 @@ nsGlobalWindow::IsChromeWindow(JSContext* aCx, JSObject* aObj)
   return xpc::WindowOrNull(aObj)->IsChromeWindow();
 }
 
-/* static */ bool
-nsGlobalWindow::IsShowModalDialogEnabled(JSContext*, JSObject*)
-{
-  static bool sAddedPrefCache = false;
-  static bool sIsDisabled;
-  static const char sShowModalDialogPref[] = "dom.disable_window_showModalDialog";
-
-  if (!sAddedPrefCache) {
-    Preferences::AddBoolVarCache(&sIsDisabled, sShowModalDialogPref, false);
-    sAddedPrefCache = true;
-  }
-
-  return !sIsDisabled;
-}
-
 nsIDOMOfflineResourceList*
 nsGlobalWindow::GetApplicationCache(ErrorResult& aError)
 {
@@ -9136,7 +9121,7 @@ nsGlobalWindow::ShowModalDialog(const nsAString& aUrl, nsIVariant* aArgument,
                             (aUrl, aArgument, aOptions, aError), aError,
                             nullptr);
 
-  if (!IsShowModalDialogEnabled()) {
+  if (Preferences::GetBool("dom.disable_window_showModalDialog", false)) {
     aError.Throw(NS_ERROR_NOT_AVAILABLE);
     return nullptr;
   }

dom/base/nsGlobalWindow.h

@@ -512,9 +512,6 @@ public:
 
   static bool IsChromeWindow(JSContext* /* unused */, JSObject* aObj);
 
-  static bool IsShowModalDialogEnabled(JSContext* /* unused */ = nullptr,
-                                       JSObject* /* unused */ = nullptr);
-
   bool DoNewResolve(JSContext* aCx, JS::Handle<JSObject*> aObj,
                     JS::Handle<jsid> aId,
                     JS::MutableHandle<JSPropertyDescriptor> aDesc);

dom/webidl/Window.webidl

@@ -79,8 +79,7 @@ typedef any Transferable;
   [Throws] DOMString? prompt(optional DOMString message = "", optional DOMString default = "");
   [Throws] void print();
   //[Throws] any showModalDialog(DOMString url, optional any argument);
-  [Throws, Func="nsGlobalWindow::IsShowModalDialogEnabled"]
-  any showModalDialog(DOMString url, optional any argument, optional DOMString options = "");
+  [Throws] any showModalDialog(DOMString url, optional any argument, optional DOMString options = "");
 
   [Throws, CrossOriginCallable] void postMessage(any message, DOMString targetOrigin, optional sequence<Transferable> transfer);