Turn an if in ~PrintPreviewDistiller() that's always true to a DCHECK.

chrome/browser/ui/webui/print_preview/print_preview_distiller.cc

 // Copyright 2015 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/ui/webui/print_preview/print_preview_distiller.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
@@ skipping 239 matching lines @@
   printing::PrintPreviewDialogController* dialog_controller =
       printing::PrintPreviewDialogController::GetInstance();
   if (!dialog_controller)
     return;
 
   dialog_controller->AddProxyDialogForWebContents(web_contents_.get(),
                                                   source_web_contents);
 }
 
 PrintPreviewDistiller::~PrintPreviewDistiller() {
-  if (web_contents_) {
-    printing::PrintPreviewDialogController* dialog_controller =
-        printing::PrintPreviewDialogController::GetInstance();
-    if (!dialog_controller)
-      return;
+  DCHECK(web_contents_);
 
-    dialog_controller->RemoveProxyDialogForWebContents(web_contents_.get());
-  }
+  printing::PrintPreviewDialogController* dialog_controller =
+      printing::PrintPreviewDialogController::GetInstance();
+  if (!dialog_controller)
+    return;
+
+  dialog_controller->RemoveProxyDialogForWebContents(web_contents_.get());
 }
 
 WebContents* PrintPreviewDistiller::CreateWebContents(
     SessionStorageNamespace* session_storage_namespace,
     WebContents* source_web_contents) {
   // TODO(ajwong): Remove the temporary map once prerendering is aware of
   // multiple session storage namespaces per tab.
   content::SessionStorageNamespaceMap session_storage_namespace_map;
   Profile* profile =
       Profile::FromBrowserContext(source_web_contents->GetBrowserContext());
   session_storage_namespace_map[std::string()] = session_storage_namespace;
   return WebContents::CreateWithSessionStorage(
       WebContents::CreateParams(profile), session_storage_namespace_map);
 }