sync: Add non-blocking type encryption support

sync/engine/model_type_sync_proxy_impl.h

Index: sync/engine/model_type_sync_proxy_impl.h
diff --git a/sync/engine/model_type_sync_proxy_impl.h b/sync/engine/model_type_sync_proxy_impl.h
index 2390eda072e0b8840604c118101b5af0d03b56dc..4cf05bd56c885df168be6dea6c9a8a3188c3e9aa 100644
--- a/sync/engine/model_type_sync_proxy_impl.h
+++ b/sync/engine/model_type_sync_proxy_impl.h
@@ -73,7 +73,16 @@ class SYNC_EXPORT_PRIVATE ModelTypeSyncProxyImpl : base::NonThreadSafe {
   // Informs this object that there are some incoming updates is should
   // handle.
   void OnUpdateReceived(const DataTypeState& type_state,
-                        const UpdateResponseDataList& response_list);
+                        const UpdateResponseDataList& response_list,
+                        const UpdateResponseDataList& inapplicable_updates);
+
+  // Returns the list of inapplicable updates.
+  //
+  // This is used as a helper function, but it's public mainly for testing.
+  // The current test harness setup doesn't allow us to test the data that the
+  // proxy sends to the worker during initialization, so we use this to inspect
+  // its state instead.
+  UpdateResponseDataList GetInapplicableUpdates();
 
   // Returns the long-lived WeakPtr that is intended to be registered with the
   // ProfileSyncService.
@@ -81,6 +90,7 @@ class SYNC_EXPORT_PRIVATE ModelTypeSyncProxyImpl : base::NonThreadSafe {
 
  private:
   typedef std::map<std::string, ModelTypeEntity*> EntityMap;
+  typedef std::map<std::string, UpdateResponseData*> UpdateMap;
 
   // Sends all commit requests that are due to be sent to the sync thread.
   void FlushPendingCommitRequests();
@@ -123,6 +133,12 @@ class SYNC_EXPORT_PRIVATE ModelTypeSyncProxyImpl : base::NonThreadSafe {
   EntityMap entities_;
   STLValueDeleter<EntityMap> entities_deleter_;
 
+  // A set of updates that can not be applied at this time.  These are never
+  // used by the model.  They are kept here only so we can save and restore
+  // them across restarts, and keep them in sync with our progress markers.
+  UpdateMap inapplicable_updates_;
+  STLValueDeleter<UpdateMap> inapplicable_updates_deleter_;

[stanisc, 2014/07/30 00:30:04]

Since we seem to be using this map/deleted pair a lot, does it make sense to
introduce a class that combines both? We don't have to do that as a part of this
change but you should consider filing a bug.

[rlarocque, 2014/07/30 21:56:01]

Done: crbug.com/398944

+
   // We use two different WeakPtrFactories because we want the pointers they
   // issue to have different lifetimes.  When asked to disconnect from the sync
   // thread, we want to make sure that no tasks generated as part of the