commit 315fe73694f9
Author: Matt Woodrow <mwoodrow@mozilla.com>
Date:   Tue Nov 14 10:31:36 2017 +1300

    Bug 1261175. r=bobowen a=gchang
    
    MozReview-Commit-ID: B9yAN0F01rj
    
    --HG--
    extra : amend_source : 7585df8257930896070ddcb64c93a28a39fbbee7
---
 layout/base/nsDocumentViewer.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git layout/base/nsDocumentViewer.cpp layout/base/nsDocumentViewer.cpp
index be33cf990d91..4fe03d3f7f88 100644
--- layout/base/nsDocumentViewer.cpp
+++ layout/base/nsDocumentViewer.cpp
@@ -549,6 +549,12 @@ nsDocumentViewer::~nsDocumentViewer()
     mDocument->Destroy();
   }
 
+  if (mPrintEngine) {
+    mPrintEngine->Destroy();
+    mPrintEngine = nullptr;
+  }
+
+  MOZ_RELEASE_ASSERT(mDestroyRefCount == 0);
   NS_ASSERTION(!mPresShell && !mPresContext,
                "User did not call nsIContentViewer::Destroy");
   if (mPresShell || mPresContext) {