Replace deprecated base::NonThreadSafe in components/policy in favor of SequenceChecker.

components/policy/core/common/async_policy_provider.h

Index: components/policy/core/common/async_policy_provider.h
diff --git a/components/policy/core/common/async_policy_provider.h b/components/policy/core/common/async_policy_provider.h
index 56eb9bf9869e2734716ff78f6bb6d6fa827c4348..3ef4c4b0bf01c67d4e8a19f54fa133b04568ceec 100644
--- a/components/policy/core/common/async_policy_provider.h
+++ b/components/policy/core/common/async_policy_provider.h
@@ -11,7 +11,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "components/policy/core/common/configuration_policy_provider.h"
 #include "components/policy/policy_export.h"
 
@@ -28,8 +28,7 @@ class SchemaRegistry;
 // A policy provider that loads its policies asynchronously on a background
 // thread. Platform-specific providers are created by passing an implementation
 // of AsyncPolicyLoader to a new AsyncPolicyProvider.
-class POLICY_EXPORT AsyncPolicyProvider : public ConfigurationPolicyProvider,
-                                          public base::NonThreadSafe {
+class POLICY_EXPORT AsyncPolicyProvider : public ConfigurationPolicyProvider {
  public:
   // The AsyncPolicyProvider does a synchronous load in its constructor, and
   // therefore it needs the |registry| at construction time. The same |registry|
@@ -67,6 +66,8 @@ class POLICY_EXPORT AsyncPolicyProvider : public ConfigurationPolicyProvider,
   // thread. See the implementation for the details.
   base::CancelableClosure refresh_callback_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   // Used to get a WeakPtr to |this| for the update callback given to the
   // loader.
   base::WeakPtrFactory<AsyncPolicyProvider> weak_factory_;