Using PolicyServiceWatcher instead of PolicyWatcherLinux/Win/Mac.

components/policy/core/common/policy_service_impl.h

Index: components/policy/core/common/policy_service_impl.h
diff --git a/components/policy/core/common/policy_service_impl.h b/components/policy/core/common/policy_service_impl.h
index e74141a6bd9b766443d8b991268c9f5b10ca4a96..56f5675eb1d4d3293d3469e4ab07bfadd5a5e727 100644
--- a/components/policy/core/common/policy_service_impl.h
+++ b/components/policy/core/common/policy_service_impl.h
@@ -14,6 +14,7 @@
 #include "base/callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "base/threading/thread_checker.h"
 #include "components/policy/core/common/configuration_policy_provider.h"
 #include "components/policy/core/common/policy_bundle.h"
 #include "components/policy/core/common/policy_service.h"
@@ -90,6 +91,9 @@ class POLICY_EXPORT PolicyServiceImpl
   // RefreshPolicies() call.
   std::vector<base::Closure> refresh_callbacks_;
 
+  // Used to verify thread-safe usage.
+  base::ThreadChecker thread_checker_;
+
   // Used to create tasks to delay new policy updates while we may be already
   // processing previous policy updates.
   base::WeakPtrFactory<PolicyServiceImpl> update_task_ptr_factory_;