Make sync's change processors sequence-affine.

components/sync/driver/generic_change_processor.cc

Index: components/sync/driver/generic_change_processor.cc
diff --git a/components/sync/driver/generic_change_processor.cc b/components/sync/driver/generic_change_processor.cc
index 47f6217c88bbf24ea4fce0cab982395fe83854af..1dee59fda337dfbdee48bb11ed9df1a63826b28d 100644
--- a/components/sync/driver/generic_change_processor.cc
+++ b/components/sync/driver/generic_change_processor.cc
@@ -13,7 +13,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/threading/thread_task_runner_handle.h"
+#include "base/threading/sequenced_task_runner_handle.h"
 #include "components/sync/base/unrecoverable_error_handler.h"
 #include "components/sync/driver/sync_api_component_factory.h"
 #include "components/sync/driver/sync_client.h"
@@ -119,7 +119,7 @@ GenericChangeProcessor::GenericChangeProcessor(
       merge_result_(merge_result),
       share_handle_(user_share),
       weak_ptr_factory_(this) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DCHECK_NE(type_, UNSPECIFIED);
   if (attachment_store) {
     std::string store_birthday;
@@ -135,25 +135,25 @@ GenericChangeProcessor::GenericChangeProcessor(
         base::MakeUnique<base::WeakPtrFactory<AttachmentService>>(
             attachment_service_.get());
     attachment_service_proxy_ = AttachmentServiceProxy(
-        base::ThreadTaskRunnerHandle::Get(),
+        base::SequencedTaskRunnerHandle::Get(),
         attachment_service_weak_ptr_factory_->GetWeakPtr());
     UploadAllAttachmentsNotOnServer();
   } else {
     attachment_service_proxy_ =
-        AttachmentServiceProxy(base::ThreadTaskRunnerHandle::Get(),
+        AttachmentServiceProxy(base::SequencedTaskRunnerHandle::Get(),
                                base::WeakPtr<AttachmentService>());
   }
 }
 
 GenericChangeProcessor::~GenericChangeProcessor() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
 }
 
 void GenericChangeProcessor::ApplyChangesFromSyncModel(
     const BaseTransaction* trans,
     int64_t model_version,
     const ImmutableChangeRecordList& changes) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DCHECK(syncer_changes_.empty());
   for (ChangeRecordList::const_iterator it = changes.Get().begin();
        it != changes.Get().end(); ++it) {
@@ -194,7 +194,7 @@ void GenericChangeProcessor::ApplyChangesFromSyncModel(
 }
 
 void GenericChangeProcessor::CommitChangesFromSyncModel() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   if (syncer_changes_.empty())
     return;
   if (!local_service_.get()) {
@@ -258,7 +258,7 @@ void GenericChangeProcessor::OnAttachmentUploaded(
 
 SyncError GenericChangeProcessor::GetAllSyncDataReturnError(
     SyncDataList* current_sync_data) const {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   std::string type_name = ModelTypeToString(type_);
   ReadTransaction trans(FROM_HERE, share_handle());
   ReadNode root(&trans);
@@ -424,7 +424,7 @@ SyncError GenericChangeProcessor::AttemptDelete(
 SyncError GenericChangeProcessor::ProcessSyncChanges(
     const tracked_objects::Location& from_here,
     const SyncChangeList& list_of_changes) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
 
   if (list_of_changes.empty()) {
     // No work. Exit without entering WriteTransaction.
@@ -644,7 +644,7 @@ SyncError GenericChangeProcessor::HandleActionUpdate(
 }
 
 bool GenericChangeProcessor::SyncModelHasUserCreatedNodes(bool* has_nodes) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DCHECK(has_nodes);
   std::string type_name = ModelTypeToString(type_);
   std::string err_str =
@@ -665,7 +665,7 @@ bool GenericChangeProcessor::SyncModelHasUserCreatedNodes(bool* has_nodes) {
 }
 
 bool GenericChangeProcessor::CryptoReadyIfNecessary() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   // We only access the cryptographer while holding a transaction.
   ReadTransaction trans(FROM_HERE, share_handle());
   const ModelTypeSet encrypted_types = trans.GetEncryptedTypes();
@@ -675,12 +675,12 @@ bool GenericChangeProcessor::CryptoReadyIfNecessary() {
 void GenericChangeProcessor::StartImpl() {}
 
 UserShare* GenericChangeProcessor::share_handle() const {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   return share_handle_;
 }
 
 void GenericChangeProcessor::UploadAllAttachmentsNotOnServer() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DCHECK(attachment_service_.get());
   AttachmentIdList ids;
   {