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

sync/syncable/entry_kernel.h

Index: sync/syncable/entry_kernel.h
diff --git a/sync/syncable/entry_kernel.h b/sync/syncable/entry_kernel.h
index 9314797faf7438bcbdf1a9dd386c6d088d27ad2a..fba1b8819936f620ad220472d5f4fec8183ec490 100644
--- a/sync/syncable/entry_kernel.h
+++ b/sync/syncable/entry_kernel.h
@@ -15,6 +15,7 @@
 #include "sync/syncable/syncable_id.h"
 #include "sync/util/time.h"
 
+namespace syncer {
 namespace syncable {
 
 // Things you need to update if you change any of the fields below:
@@ -319,5 +320,6 @@ base::ListValue* EntryKernelMutationMapToValue(
     const EntryKernelMutationMap& mutations);
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif // SYNC_SYNCABLE_ENTRY_KERNEL_H_