[Sync] Move sync/{internal_api,syncable} into syncer namespace

sync/sessions/sync_session_context.h

Index: sync/sessions/sync_session_context.h
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index ab54042e61a87c351540db3239b0a8016bf77198..8edc18fc2aa7508ed800c408727c7174059bf07a 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -30,10 +30,6 @@
 #include "sync/internal_api/public/engine/model_safe_worker.h"
 #include "sync/sessions/debug_info_getter.h"
 
-namespace syncable {
-class Directory;
-}
-
 namespace syncer {
 
 class ConflictResolver;
@@ -41,6 +37,10 @@ class ExtensionsActivityMonitor;
 class ServerConnectionManager;
 class ThrottledDataTypeTracker;
 
+namespace syncable {
+class Directory;
+}
+
 // Default number of items a client can commit in a single message.
 static const int kDefaultMaxCommitBatchSize = 25;