Remove some WebContents::GetRenderViewHost() calls.

chrome/browser/printing/background_printing_manager.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/background_printing_manager.h"
 
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
@@ skipping 94 matching lines @@
     // this case is hit, someone else won the race, so there is no need to
     // continue. <http://crbug.com/100806>
     return;
   }
 
   // Stop all observation ...
   registrar_.Remove(this, chrome::NOTIFICATION_PRINT_JOB_RELEASED,
                     content::Source<WebContents>(preview_contents));
   printing_contents_map_.erase(i);
 
-  // ... and mortally wound the contents. (Deletion immediately is not a good
-  // idea in case this was called from RenderViewGone.)
+  // ... and mortally wound the contents. Deletion immediately is not a good
+  // idea in case this was triggered by |preview_contents| far up the
+  // callstack. (Trace where the NOTIFICATION_PRINT_JOB_RELEASED comes from.)
   base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, preview_contents);
 }
 
 std::set<content::WebContents*> BackgroundPrintingManager::CurrentContentSet() {
   std::set<content::WebContents*> result;
   for (const auto& entry : printing_contents_map_)
     result.insert(entry.first);
 
   return result;
 }
 
 bool BackgroundPrintingManager::HasPrintPreviewDialog(
     WebContents* preview_dialog) {
   return base::ContainsKey(printing_contents_map_, preview_dialog);
 }
 
 }  // namespace printing