Add checks for android printing

chrome/browser/printing/print_job_worker.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 "chrome/browser/printing/print_job_worker.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
@@ skipping 201 matching lines @@
     bool has_selection,
     bool is_scripted) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
 #if defined(OS_ANDROID)
   if (is_scripted) {
     PrintingContextDelegate* printing_context_delegate =
         static_cast<PrintingContextDelegate*>(printing_context_delegate_.get());
     content::WebContents* web_contents =
         printing_context_delegate->GetWebContents();
-    TabAndroid* tab = TabAndroid::FromWebContents(web_contents);
+    TabAndroid* tab =
+        web_contents ? TabAndroid::FromWebContents(web_contents) : nullptr;
 
     // Regardless of whether the following call fails or not, the javascript
     // call will return since startPendingPrint will make it return immediately
     // in case of error.
     if (tab)
       tab->SetPendingPrint();
   }
 #endif
 
   // weak_factory_ creates pointers valid only on owner_ thread.
@@ skipping 201 matching lines @@
                               document_,
                               scoped_refptr<PrintedPage>()));
   Cancel();
 
   // Makes sure the variables are reinitialized.
   document_ = NULL;
   page_number_ = PageNumber::npos();
 }
 
 }  // namespace printing