Try to more gracefully handle unexpected destruction of stylesheet linking

nodes.  Bug 185808 (just fixes the crash, not the real problem).  r=sicking,
sr=jst, a=dbaron

content/base/src/nsGenericElement.cpp

@@ -743,6 +743,8 @@ nsGenericElement::nsGenericElement()
 
 nsGenericElement::~nsGenericElement()
 {
+  NS_PRECONDITION(!mDocument, "Please remove this from the document properly");
+  
   // pop any enclosed ranges out
   // nsRange::OwnerGone(mContent); not used for now
 
@@ -790,7 +792,7 @@ nsGenericElement::~nsGenericElement()
     delete slots;
   }
 
-  // No calling GetFlags() beond this point...
+  // No calling GetFlags() beyond this point...
 }
 
 PR_STATIC_CALLBACK(void)

content/base/src/nsStyleLinkElement.cpp

@@ -48,13 +48,22 @@ nsStyleLinkElement::nsStyleLinkElement() :
 
 nsStyleLinkElement::~nsStyleLinkElement()
 {
+  nsCOMPtr<nsICSSStyleSheet> cssSheet = do_QueryInterface(mStyleSheet);
+  if (cssSheet) {
+    cssSheet->SetOwningNode(nsnull);
+  }
 }
 
 NS_IMETHODIMP 
 nsStyleLinkElement::SetStyleSheet(nsIStyleSheet* aStyleSheet)
 {
+  nsCOMPtr<nsICSSStyleSheet> cssSheet = do_QueryInterface(mStyleSheet);
+  if (cssSheet) {
+    cssSheet->SetOwningNode(nsnull);
+  }
+
   mStyleSheet = aStyleSheet;
-  nsCOMPtr<nsICSSStyleSheet> cssSheet = do_QueryInterface(aStyleSheet);
+  cssSheet = do_QueryInterface(mStyleSheet);
   if (cssSheet) {
     nsCOMPtr<nsIDOMNode> node;
     CallQueryInterface(this,
@@ -166,6 +175,15 @@ NS_IMETHODIMP
 nsStyleLinkElement::UpdateStyleSheet(nsIDocument *aOldDocument,
                                      nsICSSLoaderObserver* aObserver)
 {
+  if (mStyleSheet && aOldDocument) {
+    // We're removing the link element from the document, unload the
+    // stylesheet.  We want to do this even if updates are disabled, since
+    // otherwise a sheet with a stale linking element pointer will be hanging
+    // around -- not good!
+    aOldDocument->RemoveStyleSheet(mStyleSheet);
+    mStyleSheet = nsnull;
+  }
+
   if (mDontLoadStyle || !mUpdatesEnabled) {
     return NS_OK;
   }
@@ -185,13 +203,6 @@ nsStyleLinkElement::UpdateStyleSheet(nsIDocument *aOldDocument,
   nsCOMPtr<nsIDocument> doc;
   thisContent->GetDocument(*getter_AddRefs(doc));
 
-  if (mStyleSheet && aOldDocument) {
-    // We're removing the link element from the document, unload the
-    // stylesheet.
-    aOldDocument->RemoveStyleSheet(mStyleSheet);
-    mStyleSheet = nsnull;
-  }
-
   if (!doc) {
     return NS_OK;
   }