Bug 1265795 P4 Always call nsDocument::SetScriptGlobalObject(nullptr)…

… from nsDocument::Destroy(). r=bz

Currently there are certain paths in nsDocumentViewer that can call
nsDocument::Destroy(), but fail to call SetScriptGlobalObject(nullptr).  This
results in the global never being cleared.

This patch refactors things so nsDocument::Destroy() always clears the global.
This ensures a more consistent document teardown since we don't rely on
external callers to get multiple method calls correct.

dom/base/nsDocument.cpp

@@ -8943,6 +8943,7 @@ nsDocument::Destroy()
 
   mIsGoingAway = true;
 
+  SetScriptGlobalObject(nullptr);
   RemovedFromDocShell();
 
   bool oldVal = mInUnlinkOrDeletion;

layout/base/nsDocumentViewer.cpp

@@ -1758,7 +1758,6 @@ nsDocumentViewer::SetDocumentInternal(nsIDocument* aDocument,
     }
 
     if (mDocument->IsStaticDocument()) {
-      mDocument->SetScriptGlobalObject(nullptr);
       mDocument->Destroy();
     }
 
@@ -4306,7 +4305,6 @@ nsDocumentViewer::OnDonePrinting()
       }
     } else if (mClosingWhilePrinting) {
       if (mDocument) {
-        mDocument->SetScriptGlobalObject(nullptr);
         mDocument->Destroy();
         mDocument = nullptr;
       }