Replace deprecated base::NonThreadSafe in extensions in favor of SequenceChecker.

extensions/browser/extension_throttle_manager.h

Index: extensions/browser/extension_throttle_manager.h
diff --git a/extensions/browser/extension_throttle_manager.h b/extensions/browser/extension_throttle_manager.h
index cad766bef4e031e99756820473ce51a63324f80e..6b4723ac096e13a5ee9a28f86c1c324d5e2d9aaf 100644
--- a/extensions/browser/extension_throttle_manager.h
+++ b/extensions/browser/extension_throttle_manager.h
@@ -11,7 +11,7 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "base/threading/platform_thread.h"
 #include "extensions/browser/extension_throttle_entry.h"
 #include "net/base/backoff_entry.h"
@@ -40,8 +40,7 @@ namespace extensions {
 // clean out outdated entries. URL ID consists of lowercased scheme, host, port
 // and path. All URLs converted to the same ID will share the same entry.
 class ExtensionThrottleManager
-    : NON_EXPORTED_BASE(public base::NonThreadSafe),
-      public net::NetworkChangeNotifier::IPAddressObserver,
+    : public net::NetworkChangeNotifier::IPAddressObserver,
       public net::NetworkChangeNotifier::ConnectionTypeObserver {
  public:
   ExtensionThrottleManager();
@@ -178,6 +177,8 @@ class ExtensionThrottleManager
   // This is NULL when it is not set for tests.
   std::unique_ptr<net::BackoffEntry::Policy> backoff_policy_for_tests_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(ExtensionThrottleManager);
 };