[Sync] Moving DataTypeState to be a proto so that it can easily be

serialized to storage by model types.

BUG=543405

Review URL: https://codereview.chromium.org/1678343002

Cr-Commit-Position: refs/heads/master@{#374667}

22 files changed, 162 insertions, 133 deletions

diff --git a/sync/api/metadata_batch.cc b/sync/api/metadata_batch.cc
index 072ad5e..a172d1e 100644
--- a/sync/api/metadata_batch.cc
+++ b/sync/api/metadata_batch.cc
@@ -18,11 +18,11 @@ void MetadataBatch::AddMetadata(const std::string& client_tag,
   metadata_map_.insert(std::make_pair(client_tag, metadata));
 }
 
-const DataTypeState& MetadataBatch::GetDataTypeState() const {
+const sync_pb::DataTypeState& MetadataBatch::GetDataTypeState() const {
   return state_;
 }
 
-void MetadataBatch::SetDataTypeState(const DataTypeState& state) {
+void MetadataBatch::SetDataTypeState(const sync_pb::DataTypeState& state) {
   state_ = state;
 }
 
diff --git a/sync/api/metadata_batch.h b/sync/api/metadata_batch.h
index 56ab2a7..dd4b8d0 100644
--- a/sync/api/metadata_batch.h
+++ b/sync/api/metadata_batch.h
@@ -6,9 +6,10 @@
 #define SYNC_API_METADATA_BATCH_H_
 
 #include <map>
+#include <string>
 
 #include "sync/base/sync_export.h"
-#include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/entity_metadata.pb.h"
 
 namespace syncer_v2 {
@@ -32,14 +33,14 @@ class SYNC_EXPORT MetadataBatch {
                    const sync_pb::EntityMetadata& metadata);
 
   // Get the DataTypeState for this batch.
-  const DataTypeState& GetDataTypeState() const;
+  const sync_pb::DataTypeState& GetDataTypeState() const;
 
   // Set the DataTypeState for this batch.
-  void SetDataTypeState(const DataTypeState& state);
+  void SetDataTypeState(const sync_pb::DataTypeState& state);
 
  private:
   EntityMetadataMap metadata_map_;
-  DataTypeState state_;
+  sync_pb::DataTypeState state_;
 };
 
 }  // namespace syncer_v2
diff --git a/sync/api/metadata_change_list.h b/sync/api/metadata_change_list.h
index a8c0d95..53c8e24 100644
--- a/sync/api/metadata_change_list.h
+++ b/sync/api/metadata_change_list.h
@@ -10,11 +10,11 @@
 #include "sync/base/sync_export.h"
 
 namespace sync_pb {
+class DataTypeState;
 class EntityMetadata;
 }  // namespace sync_pb
 
 namespace syncer_v2 {
-struct DataTypeState;
 
 // Interface used by the processor and service to communicate about metadata.
 // The purpose of the interface is to record changes to data type global and
@@ -30,7 +30,8 @@ class SYNC_EXPORT MetadataChangeList {
   virtual ~MetadataChangeList() {}
 
   // Requests DataTypeState to be updated in the storage.
-  virtual void UpdateDataTypeState(const DataTypeState& data_type_state) = 0;
+  virtual void UpdateDataTypeState(
+      const sync_pb::DataTypeState& data_type_state) = 0;
 
   // Requests DataTypeState to be cleared from the storage.
   virtual void ClearDataTypeState() = 0;
diff --git a/sync/engine/model_type_worker.cc b/sync/engine/model_type_worker.cc
index e661588..5b6e7eb 100644
--- a/sync/engine/model_type_worker.cc
+++ b/sync/engine/model_type_worker.cc
@@ -33,7 +33,7 @@ using syncer::SyncerError;
 
 ModelTypeWorker::ModelTypeWorker(
     ModelType type,
-    const DataTypeState& initial_state,
+    const sync_pb::DataTypeState& initial_state,
     const UpdateResponseDataList& saved_pending_updates,
     scoped_ptr<Cryptographer> cryptographer,
     NudgeHandler* nudge_handler,
@@ -45,7 +45,7 @@ ModelTypeWorker::ModelTypeWorker(
       nudge_handler_(nudge_handler),
       weak_ptr_factory_(this) {
   // Request an initial sync if it hasn't been completed yet.
-  if (!data_type_state_.initial_sync_done) {
+  if (!data_type_state_.initial_sync_done()) {
     nudge_handler_->NudgeForInitialDownload(type_);
   }
 
@@ -94,13 +94,13 @@ void ModelTypeWorker::UpdateCryptographer(
 void ModelTypeWorker::GetDownloadProgress(
     sync_pb::DataTypeProgressMarker* progress_marker) const {
   DCHECK(CalledOnValidThread());
-  progress_marker->CopyFrom(data_type_state_.progress_marker);
+  progress_marker->CopyFrom(data_type_state_.progress_marker());
 }
 
 void ModelTypeWorker::GetDataTypeContext(
     sync_pb::DataTypeContext* context) const {
   DCHECK(CalledOnValidThread());
-  context->CopyFrom(data_type_state_.type_context);
+  context->CopyFrom(data_type_state_.type_context());
 }
 
 SyncerError ModelTypeWorker::ProcessGetUpdatesResponse(
@@ -111,8 +111,8 @@ SyncerError ModelTypeWorker::ProcessGetUpdatesResponse(
   DCHECK(CalledOnValidThread());
 
   // TODO(rlarocque): Handle data type context conflicts.
-  data_type_state_.type_context = mutated_context;
-  data_type_state_.progress_marker = progress_marker;
+  *data_type_state_.mutable_type_context() = mutated_context;
+  *data_type_state_.mutable_progress_marker() = progress_marker;
 
   UpdateResponseDataList response_datas;
   UpdateResponseDataList pending_updates;
@@ -206,10 +206,10 @@ void ModelTypeWorker::ApplyUpdates(syncer::sessions::StatusController* status) {
   // got a response with changes_remaining == 0.  If this is our first download
   // cycle, we should update our state so the ModelTypeProcessor knows that
   // it's safe to commit items now.
-  if (!data_type_state_.initial_sync_done) {
+  if (!data_type_state_.initial_sync_done()) {
     DVLOG(1) << "Delivering 'initial sync done' ping.";
 
-    data_type_state_.initial_sync_done = true;
+    data_type_state_.set_initial_sync_done(true);
 
     model_type_processor_->OnUpdateReceived(
         data_type_state_, UpdateResponseDataList(), UpdateResponseDataList());
@@ -271,7 +271,8 @@ scoped_ptr<CommitContribution> ModelTypeWorker::GetContribution(
     return scoped_ptr<CommitContribution>();
 
   return scoped_ptr<CommitContribution>(new NonBlockingTypeCommitContribution(
-      data_type_state_.type_context, commit_entities, sequence_numbers, this));
+      data_type_state_.type_context(), commit_entities, sequence_numbers,
+      this));
 }
 
 void ModelTypeWorker::StorePendingCommit(const CommitRequestData& request) {
@@ -327,8 +328,8 @@ base::WeakPtr<ModelTypeWorker> ModelTypeWorker::AsWeakPtr() {
 }
 
 bool ModelTypeWorker::IsTypeInitialized() const {
-  return data_type_state_.initial_sync_done &&
-         !data_type_state_.progress_marker.token().empty();
+  return data_type_state_.initial_sync_done() &&
+         !data_type_state_.progress_marker().token().empty();
 }
 
 bool ModelTypeWorker::CanCommitItems() const {
@@ -392,10 +393,11 @@ void ModelTypeWorker::OnCryptographerUpdated() {
   const std::string& new_key_name = cryptographer_->GetDefaultNigoriKeyName();
 
   // Handle a change in encryption key.
-  if (data_type_state_.encryption_key_name != new_key_name) {
+  if (data_type_state_.encryption_key_name() != new_key_name) {
     DVLOG(1) << ModelTypeToString(type_) << ": Updating encryption key "
-             << data_type_state_.encryption_key_name << " -> " << new_key_name;
-    data_type_state_.encryption_key_name = new_key_name;
+             << data_type_state_.encryption_key_name() << " -> "
+             << new_key_name;
+    data_type_state_.set_encryption_key_name(new_key_name);
     new_encryption_key = true;
   }
 
diff --git a/sync/engine/model_type_worker.h b/sync/engine/model_type_worker.h
index ee6e3dc..be0430f 100644
--- a/sync/engine/model_type_worker.h
+++ b/sync/engine/model_type_worker.h
@@ -21,6 +21,7 @@
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
 #include "sync/internal_api/public/sync_encryption_handler.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/util/cryptographer.h"
 
@@ -59,7 +60,7 @@ class SYNC_EXPORT ModelTypeWorker : public syncer::UpdateHandler,
                                     public base::NonThreadSafe {
  public:
   ModelTypeWorker(syncer::ModelType type,
-                  const DataTypeState& initial_state,
+                  const sync_pb::DataTypeState& initial_state,
                   const UpdateResponseDataList& saved_pending_updates,
                   scoped_ptr<syncer::Cryptographer> cryptographer,
                   syncer::NudgeHandler* nudge_handler,
@@ -139,7 +140,7 @@ class SYNC_EXPORT ModelTypeWorker : public syncer::UpdateHandler,
   syncer::ModelType type_;
 
   // State that applies to the entire model type.
-  DataTypeState data_type_state_;
+  sync_pb::DataTypeState data_type_state_;
 
   // Pointer to the ModelTypeProcessor associated with this worker.
   // This is NULL when no proxy is connected..
diff --git a/sync/engine/model_type_worker_unittest.cc b/sync/engine/model_type_worker_unittest.cc
index cc452d8..cd19fc5 100644
--- a/sync/engine/model_type_worker_unittest.cc
+++ b/sync/engine/model_type_worker_unittest.cc
@@ -13,6 +13,7 @@
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/model_type_processor.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/sessions/status_controller.h"
 #include "sync/syncable/syncable_util.h"
@@ -84,7 +85,7 @@ class ModelTypeWorkerTest : public ::testing::Test {
       const UpdateResponseDataList& initial_pending_updates);
 
   // Initialize with a custom initial DataTypeState and pending updates.
-  void InitializeWithState(const DataTypeState& state,
+  void InitializeWithState(const sync_pb::DataTypeState& state,
                            const UpdateResponseDataList& pending_updates);
 
   // Introduce a new key that the local cryptographer can't decrypt.
@@ -148,7 +149,7 @@ class ModelTypeWorkerTest : public ::testing::Test {
   size_t GetNumModelThreadUpdateResponses() const;
   UpdateResponseDataList GetNthModelThreadUpdateResponse(size_t n) const;
   UpdateResponseDataList GetNthModelThreadPendingUpdates(size_t n) const;
-  DataTypeState GetNthModelThreadUpdateState(size_t n) const;
+  sync_pb::DataTypeState GetNthModelThreadUpdateState(size_t n) const;
 
   // Reads the latest update response datas on the model thread.
   // Note that if the model thread is in non-blocking mode, this data will not
@@ -162,7 +163,7 @@ class ModelTypeWorkerTest : public ::testing::Test {
   // be updated until the response is actually processed by the model thread.
   size_t GetNumModelThreadCommitResponses() const;
   CommitResponseDataList GetNthModelThreadCommitResponse(size_t n) const;
-  DataTypeState GetNthModelThreadCommitState(size_t n) const;
+  sync_pb::DataTypeState GetNthModelThreadCommitState(size_t n) const;
 
   // Reads the latest commit response datas on the model thread.
   // Note that if the model thread is in non-blocking mode, this data will not
@@ -243,8 +244,8 @@ ModelTypeWorkerTest::ModelTypeWorkerTest()
 ModelTypeWorkerTest::~ModelTypeWorkerTest() {}
 
 void ModelTypeWorkerTest::FirstInitialize() {
-  DataTypeState initial_state;
-  initial_state.progress_marker.set_data_type_id(
+  sync_pb::DataTypeState initial_state;
+  initial_state.mutable_progress_marker()->set_data_type_id(
       GetSpecificsFieldNumberFromModelType(kModelType));
 
   InitializeWithState(initial_state, UpdateResponseDataList());
@@ -256,12 +257,13 @@ void ModelTypeWorkerTest::NormalInitialize() {
 
 void ModelTypeWorkerTest::InitializeWithPendingUpdates(
     const UpdateResponseDataList& initial_pending_updates) {
-  DataTypeState initial_state;
-  initial_state.progress_marker.set_data_type_id(
+  sync_pb::DataTypeState initial_state;
+  initial_state.mutable_progress_marker()->set_data_type_id(
       GetSpecificsFieldNumberFromModelType(kModelType));
-  initial_state.progress_marker.set_token("some_saved_progress_token");
+  initial_state.mutable_progress_marker()->set_token(
+      "some_saved_progress_token");
 
-  initial_state.initial_sync_done = true;
+  initial_state.set_initial_sync_done(true);
 
   InitializeWithState(initial_state, initial_pending_updates);
 
@@ -269,7 +271,7 @@ void ModelTypeWorkerTest::InitializeWithPendingUpdates(
 }
 
 void ModelTypeWorkerTest::InitializeWithState(
-    const DataTypeState& state,
+    const sync_pb::DataTypeState& state,
     const UpdateResponseDataList& initial_pending_updates) {
   DCHECK(!worker_);
 
@@ -513,7 +515,7 @@ UpdateResponseDataList ModelTypeWorkerTest::GetNthModelThreadPendingUpdates(
   return mock_type_processor_->GetNthPendingUpdates(n);
 }
 
-DataTypeState ModelTypeWorkerTest::GetNthModelThreadUpdateState(
+sync_pb::DataTypeState ModelTypeWorkerTest::GetNthModelThreadUpdateState(
     size_t n) const {
   DCHECK_LT(n, GetNumModelThreadUpdateResponses());
   return mock_type_processor_->GetNthTypeStateReceivedInUpdateResponse(n);
@@ -541,7 +543,7 @@ CommitResponseDataList ModelTypeWorkerTest::GetNthModelThreadCommitResponse(
   return mock_type_processor_->GetNthCommitResponse(n);
 }
 
-DataTypeState ModelTypeWorkerTest::GetNthModelThreadCommitState(
+sync_pb::DataTypeState ModelTypeWorkerTest::GetNthModelThreadCommitState(
     size_t n) const {
   DCHECK_LT(n, GetNumModelThreadCommitResponses());
   return mock_type_processor_->GetNthTypeStateReceivedInCommitResponse(n);
@@ -768,9 +770,9 @@ TEST_F(ModelTypeWorkerTest, SendInitialSyncDone) {
   EXPECT_EQ(0U, GetNthModelThreadUpdateResponse(0).size());
   EXPECT_EQ(0U, GetNthModelThreadUpdateResponse(1).size());
 
-  const DataTypeState& state = GetNthModelThreadUpdateState(1);
-  EXPECT_FALSE(state.progress_marker.token().empty());
-  EXPECT_TRUE(state.initial_sync_done);
+  const sync_pb::DataTypeState& state = GetNthModelThreadUpdateState(1);
+  EXPECT_FALSE(state.progress_marker().token().empty());
+  EXPECT_TRUE(state.initial_sync_done());
 }
 
 // Commit two new entities in two separate commit messages.
@@ -851,7 +853,7 @@ TEST_F(ModelTypeWorkerTest, EncryptedCommit) {
 
   ASSERT_EQ(1U, GetNumModelThreadUpdateResponses());
   EXPECT_EQ(GetLocalCryptographerKeyName(),
-            GetNthModelThreadUpdateState(0).encryption_key_name);
+            GetNthModelThreadUpdateState(0).encryption_key_name());
 
   // Normal commit request stuff.
   CommitRequest("tag1", "value1");
@@ -952,7 +954,7 @@ TEST_F(ModelTypeWorkerTest, InitializeWithCryptographer) {
   // necessary.
   ASSERT_EQ(1U, GetNumModelThreadUpdateResponses());
   EXPECT_EQ(GetLocalCryptographerKeyName(),
-            GetNthModelThreadUpdateState(0).encryption_key_name);
+            GetNthModelThreadUpdateState(0).encryption_key_name());
 }
 
 // Receive updates that are initially undecryptable, then ensure they get
diff --git a/sync/internal_api/public/activation_context.h b/sync/internal_api/public/activation_context.h
index 798d851..48d9476 100644
--- a/sync/internal_api/public/activation_context.h
+++ b/sync/internal_api/public/activation_context.h
@@ -11,6 +11,7 @@
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/model_type_processor.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 
 namespace syncer_v2 {
 
@@ -21,7 +22,7 @@ struct SYNC_EXPORT ActivationContext {
   ~ActivationContext();
 
   // Initial DataTypeState at the moment of activation.
-  DataTypeState data_type_state;
+  sync_pb::DataTypeState data_type_state;
 
   // Pending updates from the previous session.
   // TODO(stanisc): crbug.com/529498: should remove pending updates.
diff --git a/sync/internal_api/public/model_type_processor.h b/sync/internal_api/public/model_type_processor.h
index 121055f..297b48f 100644
--- a/sync/internal_api/public/model_type_processor.h
+++ b/sync/internal_api/public/model_type_processor.h
@@ -8,6 +8,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 
 namespace syncer_v2 {
 class CommitQueue;
@@ -24,13 +25,13 @@ class SYNC_EXPORT ModelTypeProcessor {
   // Informs this object that some of its commit requests have been
   // successfully serviced.
   virtual void OnCommitCompleted(
-      const DataTypeState& type_state,
+      const sync_pb::DataTypeState& type_state,
       const CommitResponseDataList& response_list) = 0;
 
   // Informs this object that there are some incoming updates is should
   // handle.
   virtual void OnUpdateReceived(
-      const DataTypeState& type_state,
+      const sync_pb::DataTypeState& type_state,
       const UpdateResponseDataList& response_list,
       const UpdateResponseDataList& pending_updates) = 0;
 };
diff --git a/sync/internal_api/public/non_blocking_sync_common.cc b/sync/internal_api/public/non_blocking_sync_common.cc
index f76895c..a8ad64f 100644
--- a/sync/internal_api/public/non_blocking_sync_common.cc
+++ b/sync/internal_api/public/non_blocking_sync_common.cc
@@ -6,10 +6,6 @@
 
 namespace syncer_v2 {
 
-DataTypeState::DataTypeState() {}
-
-DataTypeState::~DataTypeState() {}
-
 CommitRequestData::CommitRequestData() {}
 
 CommitRequestData::~CommitRequestData() {}
diff --git a/sync/internal_api/public/non_blocking_sync_common.h b/sync/internal_api/public/non_blocking_sync_common.h
index 799dfca..b12ff01 100644
--- a/sync/internal_api/public/non_blocking_sync_common.h
+++ b/sync/internal_api/public/non_blocking_sync_common.h
@@ -19,32 +19,6 @@ namespace syncer_v2 {
 
 static const int64_t kUncommittedVersion = -1;
 
-// Data-type global state that must be accessed and updated on the sync thread,
-// but persisted on or through the model thread.
-struct SYNC_EXPORT DataTypeState {
-  DataTypeState();
-  ~DataTypeState();
-
-  // The latest progress markers received from the server.
-  sync_pb::DataTypeProgressMarker progress_marker;
-
-  // A data type context.  Sent to the server in every commit or update
-  // request.  May be updated by either by responses from the server or
-  // requests made on the model thread.  The interpretation of this value may
-  // be data-type specific.  Many data types ignore it.
-  sync_pb::DataTypeContext type_context;
-
-  // This value is set if this type's data should be encrypted on the server.
-  // If this key changes, the client will need to re-commit all of its local
-  // data to the server using the new encryption key.
-  std::string encryption_key_name;
-
-  // This flag is set to true when the first download cycle is complete.  The
-  // ModelTypeProcessor should not attempt to commit any items until this
-  // flag is set.
-  bool initial_sync_done = false;
-};
-
 struct SYNC_EXPORT CommitRequestData {
   CommitRequestData();
   ~CommitRequestData();
diff --git a/sync/internal_api/public/shared_model_type_processor.h b/sync/internal_api/public/shared_model_type_processor.h
index 855e964..0d8ba15 100644
--- a/sync/internal_api/public/shared_model_type_processor.h
+++ b/sync/internal_api/public/shared_model_type_processor.h
@@ -20,6 +20,7 @@
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/model_type_processor.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/sync.pb.h"
 
 namespace syncer_v2 {
@@ -85,9 +86,9 @@ class SYNC_EXPORT SharedModelTypeProcessor : public ModelTypeProcessor,
 
   // ModelTypeProcessor implementation.
   void OnConnect(scoped_ptr<CommitQueue> worker) override;
-  void OnCommitCompleted(const DataTypeState& type_state,
+  void OnCommitCompleted(const sync_pb::DataTypeState& type_state,
                          const CommitResponseDataList& response_list) override;
-  void OnUpdateReceived(const DataTypeState& type_state,
+  void OnUpdateReceived(const sync_pb::DataTypeState& type_state,
                         const UpdateResponseDataList& response_list,
                         const UpdateResponseDataList& pending_updates) override;
 
@@ -101,7 +102,7 @@ class SYNC_EXPORT SharedModelTypeProcessor : public ModelTypeProcessor,
   void FinishStart();
 
   // Handle the first update received from the server after being enabled.
-  void OnInitialUpdateReceived(const DataTypeState& type_state,
+  void OnInitialUpdateReceived(const sync_pb::DataTypeState& type_state,
                                const UpdateResponseDataList& response_list,
                                const UpdateResponseDataList& pending_updates);
 
@@ -114,7 +115,7 @@ class SYNC_EXPORT SharedModelTypeProcessor : public ModelTypeProcessor,
   void ClearTransientSyncState();
 
   syncer::ModelType type_;
-  DataTypeState data_type_state_;
+  sync_pb::DataTypeState data_type_state_;
 
   // Stores the start callback in between Start() and FinishStart().
   StartCallback start_callback_;
diff --git a/sync/internal_api/public/simple_metadata_change_list.cc b/sync/internal_api/public/simple_metadata_change_list.cc
index c1bb25f..999eda6 100644
--- a/sync/internal_api/public/simple_metadata_change_list.cc
+++ b/sync/internal_api/public/simple_metadata_change_list.cc
@@ -11,7 +11,7 @@ SimpleMetadataChangeList::SimpleMetadataChangeList() {}
 SimpleMetadataChangeList::~SimpleMetadataChangeList() {}
 
 void SimpleMetadataChangeList::UpdateDataTypeState(
-    const DataTypeState& data_type_state) {
+    const sync_pb::DataTypeState& data_type_state) {
   // TODO(skym): Implementation.
 }
 
diff --git a/sync/internal_api/public/simple_metadata_change_list.h b/sync/internal_api/public/simple_metadata_change_list.h
index aca0e69..f302b12 100644
--- a/sync/internal_api/public/simple_metadata_change_list.h
+++ b/sync/internal_api/public/simple_metadata_change_list.h
@@ -5,6 +5,8 @@
 #ifndef SYNC_INTERNAL_API_PUBLIC_SIMPLE_METADATA_CHANGE_LIST_H_
 #define SYNC_INTERNAL_API_PUBLIC_SIMPLE_METADATA_CHANGE_LIST_H_
 
+#include <string>
+
 #include "sync/api/metadata_change_list.h"
 #include "sync/api/model_type_store.h"
 #include "sync/base/sync_export.h"
@@ -19,7 +21,8 @@ class SYNC_EXPORT SimpleMetadataChangeList : public MetadataChangeList {
   SimpleMetadataChangeList();
   ~SimpleMetadataChangeList() override;
 
-  void UpdateDataTypeState(const DataTypeState& data_type_state) override;
+  void UpdateDataTypeState(
+      const sync_pb::DataTypeState& data_type_state) override;
   void ClearDataTypeState() override;
   void UpdateMetadata(const std::string& client_tag,
                       const sync_pb::EntityMetadata& metadata) override;
diff --git a/sync/internal_api/public/test/fake_metadata_change_list.h b/sync/internal_api/public/test/fake_metadata_change_list.h
index 6359602..3941f0a 100644
--- a/sync/internal_api/public/test/fake_metadata_change_list.h
+++ b/sync/internal_api/public/test/fake_metadata_change_list.h
@@ -5,10 +5,12 @@
 #ifndef SYNC_INTERNAL_API_PUBLIC_TEST_FAKE_METADATA_CHANGE_LIST_H_
 #define SYNC_INTERNAL_API_PUBLIC_TEST_FAKE_METADATA_CHANGE_LIST_H_
 
+#include <string>
 #include <vector>
 
 #include "sync/api/metadata_change_list.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/entity_metadata.pb.h"
 
 namespace syncer_v2 {
@@ -22,7 +24,8 @@ class FakeMetadataChangeList : public MetadataChangeList {
   FakeMetadataChangeList();
   ~FakeMetadataChangeList() override;
 
-  void UpdateDataTypeState(const DataTypeState& data_type_state) override;
+  void UpdateDataTypeState(
+      const sync_pb::DataTypeState& data_type_state) override;
   void ClearDataTypeState() override;
   void UpdateMetadata(const std::string& client_tag,
                       const sync_pb::EntityMetadata& metadata) override;
@@ -41,7 +44,7 @@ class FakeMetadataChangeList : public MetadataChangeList {
 
     Action action;
     std::string tag;
-    DataTypeState data_type_state;
+    sync_pb::DataTypeState data_type_state;
     sync_pb::EntityMetadata metadata;
   };
 
diff --git a/sync/internal_api/shared_model_type_processor.cc b/sync/internal_api/shared_model_type_processor.cc
index dbf7bf8..4b6b983 100644
--- a/sync/internal_api/shared_model_type_processor.cc
+++ b/sync/internal_api/shared_model_type_processor.cc
@@ -26,9 +26,9 @@ class ModelTypeProcessorProxy : public ModelTypeProcessor {
   ~ModelTypeProcessorProxy() override;
 
   void OnConnect(scoped_ptr<CommitQueue> worker) override;
-  void OnCommitCompleted(const DataTypeState& type_state,
+  void OnCommitCompleted(const sync_pb::DataTypeState& type_state,
                          const CommitResponseDataList& response_list) override;
-  void OnUpdateReceived(const DataTypeState& type_state,
+  void OnUpdateReceived(const sync_pb::DataTypeState& type_state,
                         const UpdateResponseDataList& response_list,
                         const UpdateResponseDataList& pending_updates) override;
 
@@ -51,7 +51,7 @@ void ModelTypeProcessorProxy::OnConnect(scoped_ptr<CommitQueue> worker) {
 }
 
 void ModelTypeProcessorProxy::OnCommitCompleted(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const CommitResponseDataList& response_list) {
   processor_task_runner_->PostTask(
       FROM_HERE, base::Bind(&ModelTypeProcessor::OnCommitCompleted, processor_,
@@ -59,7 +59,7 @@ void ModelTypeProcessorProxy::OnCommitCompleted(
 }
 
 void ModelTypeProcessorProxy::OnUpdateReceived(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const UpdateResponseDataList& response_list,
     const UpdateResponseDataList& pending_updates) {
   processor_task_runner_->PostTask(
@@ -101,7 +101,7 @@ void SharedModelTypeProcessor::OnMetadataLoaded(
   DCHECK(entities_.empty());
   DCHECK(!IsConnected());
 
-  if (batch->GetDataTypeState().initial_sync_done) {
+  if (batch->GetDataTypeState().initial_sync_done()) {
     EntityMetadataMap metadata_map(batch->TakeAllMetadata());
     for (auto it = metadata_map.begin(); it != metadata_map.end(); it++) {
       entities_.insert(std::make_pair(
@@ -114,7 +114,7 @@ void SharedModelTypeProcessor::OnMetadataLoaded(
     // we have data but no metadata?
   } else {
     // First time syncing; initialize metadata.
-    data_type_state_.progress_marker.set_data_type_id(
+    data_type_state_.mutable_progress_marker()->set_data_type_id(
         GetSpecificsFieldNumberFromModelType(type_));
   }
 
@@ -274,7 +274,7 @@ void SharedModelTypeProcessor::FlushPendingCommitRequests() {
     return;
 
   // Don't send anything if the type is not ready to handle commits.
-  if (!data_type_state_.initial_sync_done)
+  if (!data_type_state_.initial_sync_done())
     return;
 
   // TODO(rlarocque): Do something smarter than iterate here.
@@ -292,7 +292,7 @@ void SharedModelTypeProcessor::FlushPendingCommitRequests() {
 }
 
 void SharedModelTypeProcessor::OnCommitCompleted(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const CommitResponseDataList& response_list) {
   scoped_ptr<MetadataChangeList> change_list =
       service_->CreateMetadataChangeList();
@@ -311,9 +311,10 @@ void SharedModelTypeProcessor::OnCommitCompleted(
                    << " type: " << type_ << " client_tag: " << client_tag_hash;
       return;
     } else {
-      it->second->ReceiveCommitResponse(
-          response_data.id, response_data.sequence_number,
-          response_data.response_version, data_type_state_.encryption_key_name);
+      it->second->ReceiveCommitResponse(response_data.id,
+                                        response_data.sequence_number,
+                                        response_data.response_version,
+                                        data_type_state_.encryption_key_name());
       // TODO(stanisc): crbug.com/573333: Delete case.
       // This might be the right place to clear a metadata entry that has
       // been deleted locally and confirmed deleted by the server.
@@ -329,11 +330,10 @@ void SharedModelTypeProcessor::OnCommitCompleted(
 }
 
 void SharedModelTypeProcessor::OnUpdateReceived(
-    const DataTypeState& data_type_state,
+    const sync_pb::DataTypeState& data_type_state,
     const UpdateResponseDataList& response_list,
     const UpdateResponseDataList& pending_updates) {
-
-  if (!data_type_state_.initial_sync_done) {
+  if (!data_type_state_.initial_sync_done()) {
     OnInitialUpdateReceived(data_type_state, response_list, pending_updates);
   }
 
@@ -342,8 +342,9 @@ void SharedModelTypeProcessor::OnUpdateReceived(
   EntityChangeList entity_changes;
 
   metadata_changes->UpdateDataTypeState(data_type_state);
-  bool got_new_encryption_requirements = data_type_state_.encryption_key_name !=
-                                         data_type_state.encryption_key_name;
+  bool got_new_encryption_requirements =
+      data_type_state_.encryption_key_name() !=
+      data_type_state.encryption_key_name();
   data_type_state_ = data_type_state;
 
   for (auto list_it = response_list.begin(); list_it != response_list.end();
@@ -401,14 +402,14 @@ void SharedModelTypeProcessor::OnUpdateReceived(
 
     // If the received entity has out of date encryption, we schedule another
     // commit to fix it.
-    if (data_type_state_.encryption_key_name !=
+    if (data_type_state_.encryption_key_name() !=
         response_data.encryption_key_name) {
       DVLOG(2) << ModelTypeToString(type_) << ": Requesting re-encrypt commit "
                << response_data.encryption_key_name << " -> "
-               << data_type_state_.encryption_key_name;
+               << data_type_state_.encryption_key_name();
       auto it2 = entities_.find(client_tag_hash);
       it2->second->UpdateDesiredEncryptionKey(
-          data_type_state_.encryption_key_name);
+          data_type_state_.encryption_key_name());
     }
   }
 
@@ -435,7 +436,7 @@ void SharedModelTypeProcessor::OnUpdateReceived(
   if (got_new_encryption_requirements) {
     for (auto it = entities_.begin(); it != entities_.end(); ++it) {
       it->second->UpdateDesiredEncryptionKey(
-          data_type_state_.encryption_key_name);
+          data_type_state_.encryption_key_name());
     }
   }
 
@@ -448,7 +449,7 @@ void SharedModelTypeProcessor::OnUpdateReceived(
 }
 
 void SharedModelTypeProcessor::OnInitialUpdateReceived(
-    const DataTypeState& data_type_state,
+    const sync_pb::DataTypeState& data_type_state,
     const UpdateResponseDataList& response_list,
     const UpdateResponseDataList& pending_updates) {
   // TODO(maxbogue): crbug.com/569675: Generate metadata for all entities.
diff --git a/sync/internal_api/shared_model_type_processor_unittest.cc b/sync/internal_api/shared_model_type_processor_unittest.cc
index 741cfda..776179a 100644
--- a/sync/internal_api/shared_model_type_processor_unittest.cc
+++ b/sync/internal_api/shared_model_type_processor_unittest.cc
@@ -16,6 +16,7 @@
 #include "sync/internal_api/public/non_blocking_sync_common.h"
 #include "sync/internal_api/public/test/fake_metadata_change_list.h"
 #include "sync/internal_api/public/test/fake_model_type_service.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/syncable/syncable_util.h"
 #include "sync/test/engine/mock_commit_queue.h"
@@ -168,7 +169,7 @@ class SharedModelTypeProcessorTest : public ::testing::Test,
   MockCommitQueue* mock_queue_;
   scoped_ptr<MockCommitQueue> mock_queue_ptr_;
 
-  DataTypeState data_type_state_;
+  sync_pb::DataTypeState data_type_state_;
 
   // The last received EntityChangeList.
   scoped_ptr<EntityChangeList> entity_change_list_;
@@ -188,7 +189,7 @@ SharedModelTypeProcessorTest::SharedModelTypeProcessorTest()
 SharedModelTypeProcessorTest::~SharedModelTypeProcessorTest() {}
 
 void SharedModelTypeProcessorTest::InitializeToReadyState() {
-  data_type_state_.initial_sync_done = true;
+  data_type_state_.set_initial_sync_done(true);
   OnMetadataLoaded();
   Start();
   // TODO(maxbogue): crbug.com/569642: Remove this once entity data is loaded
@@ -261,7 +262,7 @@ void SharedModelTypeProcessorTest::DeleteItem(const std::string& tag,
 }
 
 void SharedModelTypeProcessorTest::OnInitialSyncDone() {
-  data_type_state_.initial_sync_done = true;
+  data_type_state_.set_initial_sync_done(true);
   UpdateResponseDataList empty_update_list;
 
   // TODO(stanisc): crbug/569645: replace this with loading the initial state
@@ -352,7 +353,7 @@ void SharedModelTypeProcessorTest::SuccessfulCommitResponse(
 
 void SharedModelTypeProcessorTest::UpdateDesiredEncryptionKey(
     const std::string& key_name) {
-  data_type_state_.encryption_key_name = key_name;
+  data_type_state_.set_encryption_key_name(key_name);
   type_processor()->OnUpdateReceived(data_type_state_, UpdateResponseDataList(),
                                      UpdateResponseDataList());
 }
@@ -561,7 +562,7 @@ TEST_F(SharedModelTypeProcessorTest, CreateAndModifyWithOverrides) {
   entity_data->specifics.mutable_preference()->set_value("value2");
   entity_data->non_unique_name = "name2";
   entity_data->client_tag_hash = "hash";
-  // TODO (skym): Consider removing this. The ID should never be changed by the
+  // TODO(skym): Consider removing this. The ID should never be changed by the
   // client once established.
   entity_data->id = "cid2";
 
@@ -588,7 +589,7 @@ TEST_F(SharedModelTypeProcessorTest, CreateAndModifyWithOverrides) {
   const FakeMetadataChangeList::Record& record2 = change_list.GetNthRecord(1);
   EXPECT_EQ(FakeMetadataChangeList::UPDATE_METADATA, record2.action);
   EXPECT_EQ("tag1", record2.tag);
-  // TODO (skym): Is this correct?
+  // TODO(skym): Is this correct?
   EXPECT_EQ("cid1", record2.metadata.server_id());
   EXPECT_EQ("hash", record2.metadata.client_tag_hash());
 
@@ -919,11 +920,11 @@ TEST_F(SharedModelTypeProcessorTest, DISABLED_Disable) {
   // Once we're ready to commit, all three local items should consider
   // themselves uncommitted and pending for commit.
   // TODO(maxbogue): crbug.com/569645: Fix when data is loaded.
-   EXPECT_EQ(1U, GetNumCommitRequestLists());
-   EXPECT_EQ(3U, GetNthCommitRequestList(0).size());
-   EXPECT_TRUE(HasCommitRequestForTag("tag1"));
-   EXPECT_TRUE(HasCommitRequestForTag("tag2"));
-   EXPECT_TRUE(HasCommitRequestForTag("tag3"));
+  EXPECT_EQ(1U, GetNumCommitRequestLists());
+  EXPECT_EQ(3U, GetNthCommitRequestList(0).size());
+  EXPECT_TRUE(HasCommitRequestForTag("tag1"));
+  EXPECT_TRUE(HasCommitRequestForTag("tag2"));
+  EXPECT_TRUE(HasCommitRequestForTag("tag3"));
 }
 
 // Test receipt of pending updates.
diff --git a/sync/internal_api/test/fake_metadata_change_list.cc b/sync/internal_api/test/fake_metadata_change_list.cc
index 407066d..ceba2cb 100644
--- a/sync/internal_api/test/fake_metadata_change_list.cc
+++ b/sync/internal_api/test/fake_metadata_change_list.cc
@@ -17,7 +17,7 @@ FakeMetadataChangeList::Record::Record() {}
 FakeMetadataChangeList::Record::~Record() {}
 
 void FakeMetadataChangeList::UpdateDataTypeState(
-    const DataTypeState& data_type_state) {
+    const sync_pb::DataTypeState& data_type_state) {
   Record record;
   record.action = UPDATE_DATA_TYPE_STATE;
   record.data_type_state = data_type_state;
diff --git a/sync/protocol/data_type_state.proto b/sync/protocol/data_type_state.proto
new file mode 100644
index 0000000..ffe9326
--- /dev/null
+++ b/sync/protocol/data_type_state.proto
@@ -0,0 +1,34 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+option retain_unknown_fields = true;
+
+package sync_pb;
+
+import "sync.proto";
+
+// Sync proto to store data type global metadata in model type storage.
+message DataTypeState {
+  // The latest progress markers received from the server.
+  optional DataTypeProgressMarker progress_marker = 1;
+
+  // A data type context.  Sent to the server in every commit or update
+  // request.  May be updated by either responses from the server or requests
+  // made on the model thread.  The interpretation of this value may be
+  // data-type specific.  Many data types ignore it.
+  optional DataTypeContext type_context = 2;
+
+  // This value is set if this type's data should be encrypted on the server.
+  // If this key changes, the client will need to re-commit all of its local
+  // data to the server using the new encryption key.
+  optional string encryption_key_name = 3;
+
+  // This flag is set to true when the first download cycle is complete.  The
+  // ModelTypeProcessor should not attempt to commit any items until this
+  // flag is set.
+  optional bool initial_sync_done = 4;
+}
diff --git a/sync/protocol/protocol.gypi b/sync/protocol/protocol.gypi
index 21aa65d..183b7db 100644
--- a/sync/protocol/protocol.gypi
+++ b/sync/protocol/protocol.gypi
@@ -21,6 +21,7 @@
       '<(sync_proto_sources_dir)/bookmark_specifics.proto',
       '<(sync_proto_sources_dir)/client_commands.proto',
       '<(sync_proto_sources_dir)/client_debug_info.proto',
+      '<(sync_proto_sources_dir)/data_type_state.proto',
       '<(sync_proto_sources_dir)/device_info_specifics.proto',
       '<(sync_proto_sources_dir)/dictionary_specifics.proto',
       '<(sync_proto_sources_dir)/encryption.proto',
diff --git a/sync/sessions/model_type_registry_unittest.cc b/sync/sessions/model_type_registry_unittest.cc
index d5b620e..079b37b 100644
--- a/sync/sessions/model_type_registry_unittest.cc
+++ b/sync/sessions/model_type_registry_unittest.cc
@@ -13,6 +13,7 @@
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/shared_model_type_processor.h"
 #include "sync/internal_api/public/test/fake_model_type_service.h"
+#include "sync/protocol/data_type_state.pb.h"
 #include "sync/test/engine/fake_model_worker.h"
 #include "sync/test/engine/mock_nudge_handler.h"
 #include "sync/test/engine/test_directory_setter_upper.h"
@@ -29,15 +30,15 @@ class ModelTypeRegistryTest : public ::testing::Test,
 
   ModelTypeRegistry* registry();
 
-  static syncer_v2::DataTypeState MakeInitialDataTypeState(ModelType type) {
-    syncer_v2::DataTypeState state;
-    state.progress_marker.set_data_type_id(
+  static sync_pb::DataTypeState MakeInitialDataTypeState(ModelType type) {
+    sync_pb::DataTypeState state;
+    state.mutable_progress_marker()->set_data_type_id(
         GetSpecificsFieldNumberFromModelType(type));
     return state;
   }
 
   static scoped_ptr<syncer_v2::ActivationContext> MakeActivationContext(
-      const syncer_v2::DataTypeState& data_type_state,
+      const sync_pb::DataTypeState& data_type_state,
       const syncer_v2::UpdateResponseDataList& saved_pending_updates,
       scoped_ptr<syncer_v2::ModelTypeProcessor> type_processor) {
     scoped_ptr<syncer_v2::ActivationContext> context =
diff --git a/sync/test/engine/mock_model_type_processor.cc b/sync/test/engine/mock_model_type_processor.cc
index d4249e2..c22a847 100644
--- a/sync/test/engine/mock_model_type_processor.cc
+++ b/sync/test/engine/mock_model_type_processor.cc
@@ -23,7 +23,7 @@ void MockModelTypeProcessor::OnConnect(scoped_ptr<CommitQueue> commit_queue) {
 }
 
 void MockModelTypeProcessor::OnCommitCompleted(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const CommitResponseDataList& response_list) {
   base::Closure task =
       base::Bind(&MockModelTypeProcessor::OnCommitCompletedImpl,
@@ -36,7 +36,7 @@ void MockModelTypeProcessor::OnCommitCompleted(
 }
 
 void MockModelTypeProcessor::OnUpdateReceived(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const UpdateResponseDataList& response_list,
     const UpdateResponseDataList& pending_updates) {
   base::Closure task = base::Bind(&MockModelTypeProcessor::OnUpdateReceivedImpl,
@@ -135,7 +135,8 @@ UpdateResponseDataList MockModelTypeProcessor::GetNthPendingUpdates(
   return received_pending_updates_[n];
 }
 
-DataTypeState MockModelTypeProcessor::GetNthTypeStateReceivedInUpdateResponse(
+sync_pb::DataTypeState
+MockModelTypeProcessor::GetNthTypeStateReceivedInUpdateResponse(
     size_t n) const {
   DCHECK_LT(n, GetNumUpdateResponses());
   return type_states_received_on_update_[n];
@@ -151,7 +152,8 @@ CommitResponseDataList MockModelTypeProcessor::GetNthCommitResponse(
   return received_commit_responses_[n];
 }
 
-DataTypeState MockModelTypeProcessor::GetNthTypeStateReceivedInCommitResponse(
+sync_pb::DataTypeState
+MockModelTypeProcessor::GetNthTypeStateReceivedInCommitResponse(
     size_t n) const {
   DCHECK_LT(n, GetNumCommitResponses());
   return type_states_received_on_commit_[n];
@@ -188,7 +190,7 @@ CommitResponseData MockModelTypeProcessor::GetCommitResponse(
 }
 
 void MockModelTypeProcessor::OnCommitCompletedImpl(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const CommitResponseDataList& response_list) {
   received_commit_responses_.push_back(response_list);
   type_states_received_on_commit_.push_back(type_state);
@@ -203,7 +205,7 @@ void MockModelTypeProcessor::OnCommitCompletedImpl(
 }
 
 void MockModelTypeProcessor::OnUpdateReceivedImpl(
-    const DataTypeState& type_state,
+    const sync_pb::DataTypeState& type_state,
     const UpdateResponseDataList& response_list,
     const UpdateResponseDataList& pending_updates) {
   received_update_responses_.push_back(response_list);
diff --git a/sync/test/engine/mock_model_type_processor.h b/sync/test/engine/mock_model_type_processor.h
index 120dedc8..a5a168e 100644
--- a/sync/test/engine/mock_model_type_processor.h
+++ b/sync/test/engine/mock_model_type_processor.h
@@ -16,6 +16,7 @@
 #include "base/macros.h"
 #include "sync/internal_api/public/model_type_processor.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
 
 namespace syncer_v2 {
 
@@ -37,9 +38,9 @@ class MockModelTypeProcessor : public ModelTypeProcessor {
 
   // Implementation of ModelTypeProcessor.
   void OnConnect(scoped_ptr<CommitQueue> commit_queue) override;
-  void OnCommitCompleted(const DataTypeState& type_state,
+  void OnCommitCompleted(const sync_pb::DataTypeState& type_state,
                          const CommitResponseDataList& response_list) override;
-  void OnUpdateReceived(const DataTypeState& type_state,
+  void OnUpdateReceived(const sync_pb::DataTypeState& type_state,
                         const UpdateResponseDataList& response_list,
                         const UpdateResponseDataList& pending_updates) override;
 
@@ -71,14 +72,16 @@ class MockModelTypeProcessor : public ModelTypeProcessor {
   size_t GetNumUpdateResponses() const;
   UpdateResponseDataList GetNthUpdateResponse(size_t n) const;
   UpdateResponseDataList GetNthPendingUpdates(size_t n) const;
-  DataTypeState GetNthTypeStateReceivedInUpdateResponse(size_t n) const;
+  sync_pb::DataTypeState GetNthTypeStateReceivedInUpdateResponse(
+      size_t n) const;
 
   // Getters to access the log of received commit responses.
   //
   // Does not includes repsonses that are in pending tasks.
   size_t GetNumCommitResponses() const;
   CommitResponseDataList GetNthCommitResponse(size_t n) const;
-  DataTypeState GetNthTypeStateReceivedInCommitResponse(size_t n) const;
+  sync_pb::DataTypeState GetNthTypeStateReceivedInCommitResponse(
+      size_t n) const;
 
   // Getters to access the lastest update response for a given tag_hash.
   bool HasUpdateResponse(const std::string& tag_hash) const;
@@ -92,13 +95,13 @@ class MockModelTypeProcessor : public ModelTypeProcessor {
   // Process a received commit response.
   //
   // Implemented as an Impl method so we can defer its execution in some cases.
-  void OnCommitCompletedImpl(const DataTypeState& type_state,
+  void OnCommitCompletedImpl(const sync_pb::DataTypeState& type_state,
                              const CommitResponseDataList& response_list);
 
   // Process a received update response.
   //
   // Implemented as an Impl method so we can defer its execution in some cases.
-  void OnUpdateReceivedImpl(const DataTypeState& type_state,
+  void OnUpdateReceivedImpl(const sync_pb::DataTypeState& type_state,
                             const UpdateResponseDataList& response_list,
                             const UpdateResponseDataList& pending_updates);
 
@@ -125,8 +128,8 @@ class MockModelTypeProcessor : public ModelTypeProcessor {
   std::vector<CommitResponseDataList> received_commit_responses_;
   std::vector<UpdateResponseDataList> received_update_responses_;
   std::vector<UpdateResponseDataList> received_pending_updates_;
-  std::vector<DataTypeState> type_states_received_on_update_;
-  std::vector<DataTypeState> type_states_received_on_commit_;
+  std::vector<sync_pb::DataTypeState> type_states_received_on_update_;
+  std::vector<sync_pb::DataTypeState> type_states_received_on_commit_;
 
   // Latest responses received, indexed by tag_hash.
   std::map<const std::string, CommitResponseData> commit_response_items_;