[Sync] Add plumbing of context from client to server

sync/engine/directory_commit_contribution.cc

Index: sync/engine/directory_commit_contribution.cc
diff --git a/sync/engine/directory_commit_contribution.cc b/sync/engine/directory_commit_contribution.cc
index 2fd7b30c9c148e3d4588517bdf84f256de346e8d..8c5ad3ba060830a55939a09870d99746b3d08e46 100644
--- a/sync/engine/directory_commit_contribution.cc
+++ b/sync/engine/directory_commit_contribution.cc
@@ -42,7 +42,7 @@ scoped_ptr<DirectoryCommitContribution> DirectoryCommitContribution::Build(
   }
 
   return scoped_ptr<DirectoryCommitContribution>(
-      new DirectoryCommitContribution(metahandles, entities, dir));
+      new DirectoryCommitContribution(type, metahandles, entities, dir));
 }
 
 void DirectoryCommitContribution::AddToCommitMessage(
@@ -53,6 +53,10 @@ void DirectoryCommitContribution::AddToCommitMessage(
   std::copy(entities_.begin(),
             entities_.end(),
             RepeatedPtrFieldBackInserter(commit_message->mutable_entries()));
+  sync_pb::DataTypeContext context;

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

The entities were grabbed out of the directory while a transaction was active in
the Build() function.  Would it make more sense to grab this state at that time,
too, so that we know they're in sync?

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

Done.

+  dir_->GetDataTypeContext(type_, &context);
+  if (!context.context().empty())
+    commit_message->add_client_contexts()->Swap(&context);
 }
 
 SyncerError DirectoryCommitContribution::ProcessCommitResponse(
@@ -142,10 +146,12 @@ size_t DirectoryCommitContribution::GetNumEntries() const {
 }
 
 DirectoryCommitContribution::DirectoryCommitContribution(
+    ModelType type,
     const std::vector<int64>& metahandles,
     const google::protobuf::RepeatedPtrField<sync_pb::SyncEntity>& entities,
     syncable::Directory* dir)
   : dir_(dir),
+    type_(type),
     metahandles_(metahandles),
     entities_(entities),
     entries_start_index_(0xDEADBEEF),