USS SyncContextProxy / data type activation refactoring

This refactoring prepares the code to introduction of
NonBlockingDataTypeController for USS datatypes. The goal
was to split the very large NonBlockingDataTypeController
change into a couple of smaller to make it easier to review
and verify.

The following changes are included here:
1) Introduced ActivationContext which is a structure that
   contains all arguments needed to activate a USS datatype.
   For now ActivationContext is passed via SyncContext /
   SyncContextProxy, but the goal is to pass it directly
   via BackendDataTypeConfigurer as an argument for
   ActivateNonBlockingDataType.
   ActivationContext is needed as a separate class because
   NonBlockingDataTypeController will have to receive it
   from the type processor's callback and temporarily hold
   on to it.
2) BackendDataTypeConfigurer - two activation methods are
   renamed to be directory specific and two more activation
   methods for non-blocking data types are added.
3) DataTypeController cleanup - OnModelLoaded() virtual
   method shouldn't be on the base class because it applies
   only to some of the subclasses and is never invoked via the
   base class.

BUG=515962

Review URL: https://codereview.chromium.org/1368683003

Cr-Commit-Position: refs/heads/master@{#351110}

2 files changed, 14 insertions, 6 deletions

diff --git a/sync/engine/model_type_processor_impl.cc b/sync/engine/model_type_processor_impl.cc
index 55aa73b..94e5c63 100644
--- a/sync/engine/model_type_processor_impl.cc
+++ b/sync/engine/model_type_processor_impl.cc
@@ -6,8 +6,10 @@
 
 #include "base/bind.h"
 #include "base/location.h"
+#include "base/thread_task_runner_handle.h"
 #include "sync/engine/commit_queue.h"
 #include "sync/engine/model_type_entity.h"
+#include "sync/internal_api/public/activation_context.h"
 #include "sync/internal_api/public/sync_context_proxy.h"
 #include "sync/syncable/syncable_util.h"
 
@@ -52,13 +54,16 @@ void ModelTypeProcessorImpl::Enable(
   data_type_state_.progress_marker.set_data_type_id(
       GetSpecificsFieldNumberFromModelType(type_));
 
-  UpdateResponseDataList saved_pending_updates = GetPendingUpdates();
+  scoped_ptr<ActivationContext> activation_context =
+      make_scoped_ptr(new ActivationContext);
+  activation_context->data_type_state = data_type_state_;
+  activation_context->saved_pending_updates = GetPendingUpdates();
+  activation_context->type_task_runner = base::ThreadTaskRunnerHandle::Get();
+  activation_context->type_processor = weak_ptr_factory_for_sync_.GetWeakPtr();
+
   sync_context_proxy_ = sync_context_proxy.Pass();
-  sync_context_proxy_->ConnectTypeToSync(
-      GetModelType(),
-      data_type_state_,
-      saved_pending_updates,
-      weak_ptr_factory_for_sync_.GetWeakPtr());
+  sync_context_proxy_->ConnectTypeToSync(GetModelType(),
+                                         activation_context.Pass());
 }
 
 void ModelTypeProcessorImpl::Disable() {
diff --git a/sync/engine/model_type_processor_impl_unittest.cc b/sync/engine/model_type_processor_impl_unittest.cc
index 8f57d69..5e0bc68 100644
--- a/sync/engine/model_type_processor_impl_unittest.cc
+++ b/sync/engine/model_type_processor_impl_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "sync/engine/model_type_processor_impl.h"
 
+#include "base/message_loop/message_loop.h"
 #include "sync/engine/commit_queue.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
@@ -129,6 +130,8 @@ class ModelTypeProcessorImplTest : public ::testing::Test {
   scoped_ptr<ModelTypeProcessorImpl> type_processor_;
 
   DataTypeState data_type_state_;
+  // This sets ThreadTaskRunnerHandle on the current thread.
+  base::MessageLoop message_loop_;
 };
 
 ModelTypeProcessorImplTest::ModelTypeProcessorImplTest()