Bug 1552049 - Enable XUL persistence for all system privilege docs. r=smaug

Remove the mozpersist attribute and XULDocument requirement to use XUL
persistence and allow any system privilege document to use it by default.

Differential Revision: https://phabricator.services.mozilla.com/D34602

--HG--
extra : moz-landing-system : lando

browser/base/content/browser.xhtml

@@ -70,7 +70,6 @@
         sizemode="normal"
         retargetdocumentfocus="urlbar"
         persist="screenX screenY width height sizemode"
-        mozpersist=""
         >
 
 # All JS files which are needed by browser.xhtml and other top level windows to

dom/base/Document.cpp

@@ -11023,12 +11023,8 @@ void Document::SetReadyStateInternal(ReadyState rs,
 
   if (READYSTATE_INTERACTIVE == rs) {
     if (nsContentUtils::IsSystemPrincipal(NodePrincipal())) {
-      Element* root = GetRootElement();
-      if ((root && root->HasAttr(kNameSpaceID_None, nsGkAtoms::mozpersist)) ||
-          IsXULDocument()) {
-        mXULPersist = new XULPersist(this);
-        mXULPersist->Init();
-      }
+      mXULPersist = new XULPersist(this);
+      mXULPersist->Init();
     }
   }
 

xpcom/ds/StaticAtoms.py

@@ -42,7 +42,6 @@ STATIC_ATOMS = [
     Atom("moztype", "_moz-type"),
     Atom("mozdirty", "_moz_dirty"),
     Atom("mozdisallowselectionprint", "mozdisallowselectionprint"),
-    Atom("mozpersist", "mozpersist"),
     Atom("mozdonotsend", "moz-do-not-send"),
     Atom("mozeditorbogusnode", "_moz_editor_bogus_node"),
     Atom("mozgeneratedcontentbefore", "_moz_generated_content_before"),