[Sync] Add context proto and directory support

sync/syncable/directory.cc

Index: sync/syncable/directory.cc
diff --git a/sync/syncable/directory.cc b/sync/syncable/directory.cc
index 97e7071e591da8a084cc5971f642bb8cdb23c5be..88fe94a4690de28036febc377fd010d77855450f 100644
--- a/sync/syncable/directory.cc
+++ b/sync/syncable/directory.cc
@@ -792,6 +792,22 @@ void Directory::IncrementTransactionVersion(ModelType type) {
   kernel_->persisted_info.transaction_version[type]++;
 }
 
+void Directory::GetDataTypeContext(BaseTransaction* trans,
+                                   ModelType type,
+                                   sync_pb::DataTypeContext* context) const {
+  ScopedKernelLock lock(this);
+  context->CopyFrom(kernel_->persisted_info.datatype_context[type]);
+}
+
+void Directory::SetDataTypeContext(
+    BaseWriteTransaction* trans,
+    ModelType type,
+    const sync_pb::DataTypeContext& context) {
+  ScopedKernelLock lock(this);
+  kernel_->persisted_info.datatype_context[type].CopyFrom(context);
+  kernel_->info_status = KERNEL_SHARE_INFO_DIRTY;
+}
+
 ModelTypeSet Directory::InitialSyncEndedTypes() {
   syncable::ReadTransaction trans(FROM_HERE, this);
   ModelTypeSet protocol_types = ProtocolTypes();