Replace deprecated base::NonThreadSafe in content/shell in favor of SequenceChecker.

content/shell/browser/layout_test/blink_test_controller.h

Index: content/shell/browser/layout_test/blink_test_controller.h
diff --git a/content/shell/browser/layout_test/blink_test_controller.h b/content/shell/browser/layout_test/blink_test_controller.h
index bb391687386a35c720ea82b23564e62a16c723f7..a96d88844c84626b5f93bbb689198eccb86087b9 100644
--- a/content/shell/browser/layout_test/blink_test_controller.h
+++ b/content/shell/browser/layout_test/blink_test_controller.h
@@ -15,8 +15,8 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/scoped_observer.h"
+#include "base/sequence_checker.h"
 #include "base/synchronization/lock.h"
-#include "base/threading/non_thread_safe.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "content/public/browser/bluetooth_chooser.h"
@@ -113,8 +113,7 @@ class BlinkTestResultPrinter {
   DISALLOW_COPY_AND_ASSIGN(BlinkTestResultPrinter);
 };
 
-class BlinkTestController : public base::NonThreadSafe,
-                            public WebContentsObserver,
+class BlinkTestController : public WebContentsObserver,
                             public RenderProcessHostObserver,
                             public NotificationObserver,
                             public GpuDataManagerObserver {
@@ -299,6 +298,8 @@ class BlinkTestController : public base::NonThreadSafe,
   ScopedAllowWaitForAndroidLayoutTests reduced_restrictions_;
 #endif
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(BlinkTestController);
 };