Bug 830236 (follow-up) - Keep the print engine when printing finished inside Print Preview. Make nsPrintEngine::DestroyPrintingData re-entrancy safe. r=cam

layout/base/nsDocumentViewer.cpp

@@ -4263,10 +4263,10 @@ nsDocumentViewer::OnDonePrinting()
 #if defined(NS_PRINTING) && defined(NS_PRINT_PREVIEW)
   if (mPrintEngine) {
     nsRefPtr<nsPrintEngine> pe = mPrintEngine;
-    mPrintEngine = nullptr;
     if (GetIsPrintPreview()) {
       pe->DestroyPrintingData();
     } else {
+      mPrintEngine = nullptr;
       pe->Destroy();
     }
 

layout/printing/nsPrintEngine.cpp

@@ -279,8 +279,9 @@ void nsPrintEngine::Destroy()
 void nsPrintEngine::DestroyPrintingData()
 {
   if (mPrt) {
-    delete mPrt;
+    nsPrintData* data = mPrt;
     mPrt = nullptr;
+    delete data;
   }
 }