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

components/policy/core/common/schema_registry.cc

Index: components/policy/core/common/schema_registry.cc
diff --git a/components/policy/core/common/schema_registry.cc b/components/policy/core/common/schema_registry.cc
index eb447b848f44dd67954ba6e0f8ff95aea48f1ed6..5b282b6c9f935295659a55a4dae1e1826bee7d5d 100644
--- a/components/policy/core/common/schema_registry.cc
+++ b/components/policy/core/common/schema_registry.cc
@@ -22,6 +22,7 @@ SchemaRegistry::SchemaRegistry() : schema_map_(new SchemaMap) {
 }
 
 SchemaRegistry::~SchemaRegistry() {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

[emaxx, 2017/05/30 10:54:39]

(note for myself) We need to also add the DCHECKs into other methods of this
class. Filed a bug https://crbug.com/727645 for that.

   for (auto& observer : internal_observers_)
     observer.OnSchemaRegistryShuttingDown(this);
 }