[Sync] Add plumbing of context from client to server

sync/engine/directory_update_handler.cc

Index: sync/engine/directory_update_handler.cc
diff --git a/sync/engine/directory_update_handler.cc b/sync/engine/directory_update_handler.cc
index 9d97765195fc1064861d9cef1064b90d276b2a6d..a2cc73c1b50632ed892353aa234903a84a1a1e19 100644
--- a/sync/engine/directory_update_handler.cc
+++ b/sync/engine/directory_update_handler.cc
@@ -31,6 +31,11 @@ void DirectoryUpdateHandler::GetDownloadProgress(
   dir_->GetDownloadProgress(type_, progress_marker);
 }
 
+void DirectoryUpdateHandler::GetDataTypeContext(
+    sync_pb::DataTypeContext* context) const {
+  dir_->GetDataTypeContext(type_, context);
+}
+
 void DirectoryUpdateHandler::ProcessGetUpdatesResponse(
     const sync_pb::DataTypeProgressMarker& progress_marker,
     const SyncEntityList& applicable_updates,
@@ -44,6 +49,20 @@ void DirectoryUpdateHandler::ProcessGetUpdatesResponse(
   }
 }
 
+void DirectoryUpdateHandler::ProcessDataTypeContextMutation(

[rlarocque, 2014/04/03 17:31:58]

Does the context need to be updated atomically with the progress markers?  If
so, then this should be merged into ProcessGetUpdatesResponse.

[Nicolas Zea, 2014/04/03 22:56:47]

Done.

+    const sync_pb::DataTypeContext& mutated_context) {
+  sync_pb::DataTypeContext local_context;
+  dir_->GetDataTypeContext(type_, &local_context);
+
+  // Only update the local context if it is still relevant. If the local version
+  // is higher, it means a local change happened while the mutation was in
+  // flight, and the local context takes priority.
+  if (mutated_context.version() >= local_context.version()) {
+    dir_->SetDataTypeContext(type_, mutated_context);
+    // TODO(zea): trigger the datatype's UpdateDataTypeContext method.
+  }
+}
+
 void DirectoryUpdateHandler::ApplyUpdates(sessions::StatusController* status) {
   if (!IsApplyUpdatesRequired()) {
     return;