One more check for PrintWebViewHelper validity.

components/printing/renderer/print_web_view_helper.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/printing/renderer/print_web_view_helper.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 966 matching lines @@
 bool PrintWebViewHelper::OnMessageReceived(const IPC::Message& message) {
   // The class is not designed to handle recursive messages. This is not
   // expected during regular flow. However, during rendering of content for
   // printing, lower level code may run nested message loop. E.g. PDF may has
   // script to show message box http://crbug.com/502562. In that moment browser
   // may receive updated printer capabilities and decide to restart print
   // preview generation. When this happened message handling function may
   // choose to ignore message or safely crash process.
   ++ipc_nesting_level_;
 
+  auto self = weak_ptr_factory_.GetWeakPtr();
+
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(PrintWebViewHelper, message)
 #if BUILDFLAG(ENABLE_BASIC_PRINTING)
     IPC_MESSAGE_HANDLER(PrintMsg_PrintPages, OnPrintPages)
     IPC_MESSAGE_HANDLER(PrintMsg_PrintForSystemDialog, OnPrintForSystemDialog)
 #endif  // BUILDFLAG(ENABLE_BASIC_PRINTING)
 #if BUILDFLAG(ENABLE_BASIC_PRINTING) && BUILDFLAG(ENABLE_PRINT_PREVIEW)
     IPC_MESSAGE_HANDLER(PrintMsg_PrintForPrintPreview, OnPrintForPrintPreview)
 #endif
 #if BUILDFLAG(ENABLE_PRINT_PREVIEW)
     IPC_MESSAGE_HANDLER(PrintMsg_InitiatePrintPreview, OnInitiatePrintPreview)
     IPC_MESSAGE_HANDLER(PrintMsg_PrintPreview, OnPrintPreview)
     IPC_MESSAGE_HANDLER(PrintMsg_PrintingDone, OnPrintingDone)
 #endif  // BUILDFLAG(ENABLE_PRINT_PREVIEW)
     IPC_MESSAGE_HANDLER(PrintMsg_SetPrintingEnabled, OnSetPrintingEnabled)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
-  --ipc_nesting_level_;
+  // Check if |this| is still valid. e.g. when OnPrintPages() returns.
+  if (self)
+    --ipc_nesting_level_;
   return handled;
 }
 
 void PrintWebViewHelper::OnDestruct() {
   delete this;
 }
 
 #if BUILDFLAG(ENABLE_BASIC_PRINTING)
 void PrintWebViewHelper::OnPrintPages() {
   if (ipc_nesting_level_> 1)
@@ skipping 1322 matching lines @@
       blink::WebConsoleMessage::LevelWarning, message));
   return false;
 }
 
 void PrintWebViewHelper::ScriptingThrottler::Reset() {
   // Reset counter on successful print.
   count_ = 0;
 }
 
 }  // namespace printing