Replace deprecated base::NonThreadSafe in chrome/browser/printing in favor of SequenceChecker.

Note to crash team: This CL is a refactor and has no intended behavior change.

This change was scripted by https://crbug.com/676387#c8.

Note-worthy for the reviewer:
 * SequenceChecker enforces thread-safety but not thread-affinity!
   If the classes that were updated are thread-affine (use thread local
   storage or a third-party API that does) they should be migrated to
   ThreadChecker instead.
 * ~NonThreadSafe() used to implcitly check in its destructor
   ~Sequence/ThreadChecker() doesn't by design. To keep this CL a
   no-op, an explicit check was added to the destructor of migrated
   classes.
 * NonThreadSafe used to provide access to subclasses, as such
   the |sequence_checker_| member was made protected rather than
   private where necessary.

BUG=676387
This CL was uploaded by git cl split.

Review-Url: https://codereview.chromium.org/2908273002
Cr-Commit-Position: refs/heads/master@{#476413}

chrome/browser/printing/background_printing_manager.cc

@@ -56,7 +56,7 @@ BackgroundPrintingManager::BackgroundPrintingManager() {
 }
 
 BackgroundPrintingManager::~BackgroundPrintingManager() {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   // The might be some WebContentses still in |printing_contents_map_| at this
   // point (e.g. when the last remaining tab closes and there is still a print
   // preview WebContents trying to print). In such a case it will fail to print,
@@ -66,7 +66,7 @@ BackgroundPrintingManager::~BackgroundPrintingManager() {
 
 void BackgroundPrintingManager::OwnPrintPreviewDialog(
     WebContents* preview_dialog) {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(PrintPreviewDialogController::IsPrintPreviewDialog(preview_dialog));
   CHECK(!HasPrintPreviewDialog(preview_dialog));
 

chrome/browser/printing/background_printing_manager.h

@@ -11,7 +11,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
@@ -26,8 +26,7 @@ namespace printing {
 // The hidden WebContents are no longer part of any Browser / TabStripModel.
 // The WebContents started life as a ConstrainedWebDialog.
 // They get deleted when the printing finishes.
-class BackgroundPrintingManager : public base::NonThreadSafe,
-                                  public content::NotificationObserver {
+class BackgroundPrintingManager : public content::NotificationObserver {
  public:
   class Observer;
 
@@ -65,6 +64,8 @@ class BackgroundPrintingManager : public base::NonThreadSafe,
 
   content::NotificationRegistrar registrar_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(BackgroundPrintingManager);
 };