[Sync] Fix test support targets + duplicate namespaces.

components/sync/engine_impl/model_type_registry.h

Index: components/sync/engine_impl/model_type_registry.h
diff --git a/components/sync/engine_impl/model_type_registry.h b/components/sync/engine_impl/model_type_registry.h
index 2e21774783e0c40156e005f9bb374cebf3facd83..9e4ce33e8a7be4550676bcf525528740c601be02 100644
--- a/components/sync/engine_impl/model_type_registry.h
+++ b/components/sync/engine_impl/model_type_registry.h
@@ -22,23 +22,20 @@
 #include "components/sync/engine_impl/nudge_handler.h"
 
 namespace syncer {
+
+class CommitContributor;
+class DirectoryCommitContributor;
+class DirectoryTypeDebugInfoEmitter;
+class DirectoryUpdateHandler;
 class ModelTypeProcessor;
 class ModelTypeWorker;
+class UpdateHandler;
 struct ModelTypeState;
-}
-
-namespace syncer {
 
 namespace syncable {
 class Directory;
 }  // namespace syncable
 
-class CommitContributor;
-class DirectoryCommitContributor;
-class DirectoryUpdateHandler;
-class DirectoryTypeDebugInfoEmitter;
-class UpdateHandler;
-
 typedef std::map<ModelType, UpdateHandler*> UpdateHandlerMap;
 typedef std::map<ModelType, CommitContributor*> CommitContributorMap;
 typedef std::map<ModelType, DirectoryTypeDebugInfoEmitter*>