sync: Add non-blocking type encryption support

sync/engine/model_type_entity.h

Index: sync/engine/model_type_entity.h
diff --git a/sync/engine/model_type_entity.h b/sync/engine/model_type_entity.h
index abc67a95a4d3026dfc455e04bb5df8cdb4b0f75c..40c78755096107bbd023299c28b592906a921cb8 100644
--- a/sync/engine/model_type_entity.h
+++ b/sync/engine/model_type_entity.h
@@ -46,7 +46,8 @@ class SYNC_EXPORT_PRIVATE ModelTypeEntity {
       const sync_pb::EntitySpecifics& specifics,
       bool deleted,
       base::Time ctime,
-      base::Time mtime);
+      base::Time mtime,
+      const std::string& encryption_key_name);
 
   // TODO(rlarocque): Implement FromDisk constructor when we implement storage.
 
@@ -79,11 +80,17 @@ class SYNC_EXPORT_PRIVATE ModelTypeEntity {
   void ApplyUpdateFromServer(int64 update_version,
                              bool deleted,
                              const sync_pb::EntitySpecifics& specifics,
-                             base::Time mtime);
+                             base::Time mtime,
+                             const std::string& encryption_key_name);
 
   // Applies a local change to this item.
   void MakeLocalChange(const sync_pb::EntitySpecifics& specifics);
 
+  // Schedule a commit if the |name| does not match this item's last known
+  // encryption key.  The worker that performs the commit is expected to
+  // encrypt the item using the latest available key.
+  void RequireEncryptionKey(const std::string& name);

[Nicolas Zea, 2014/07/30 00:34:16]

Seems odd that a method called "RequireEncryptionKey" would schedule a commit.
When is this expected to be called?

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

When the ModelTypeSyncProxy receives a new encryption key, it will call this
method on all of its items.  If the item's encryption key does not match, it
"sets the unsynced bit" for that item.

This method does not directly request a commit, but it does ensure the item will
be picked up in the next commit batch, which should happen soon after.

Not sure what a better name would be.  Something like
"MarkForCommitIfEncryptionKeyIsOld" would work, but it's a bit long.  I'm
looking for something more concise. 

[Nicolas Zea, 2014/07/31 18:06:26]

How about just UpdateServerEncryptionKey?

[rlarocque, 2014/07/31 18:14:37]

UpdateDesiredServerEncryptionKey?  The actual update happens later, on a
different thread.

[rlarocque, 2014/07/31 18:54:04]

Done.

+
   // Applies a local deletion to this item.
   void Delete();
 
@@ -104,7 +111,8 @@ class SYNC_EXPORT_PRIVATE ModelTypeEntity {
   // reached the server.
   void ReceiveCommitResponse(const std::string& id,
                              int64 sequence_number,
-                             int64 response_version);
+                             int64 response_version,
+                             const std::string& encryption_key_name);
 
   // Clears any in-memory sync state associated with outstanding commits.
   void ClearTransientSyncState();
@@ -124,7 +132,8 @@ class SYNC_EXPORT_PRIVATE ModelTypeEntity {
                   const sync_pb::EntitySpecifics& specifics,
                   bool deleted,
                   base::Time ctime,
-                  base::Time mtime);
+                  base::Time mtime,
+                  const std::string& encryption_key_name);
 
   // A sequence number used to track in-progress commits.  Each local change
   // increments this number.
@@ -185,6 +194,10 @@ class SYNC_EXPORT_PRIVATE ModelTypeEntity {
   // doesn't bother to inspect their values.
   base::Time ctime_;
   base::Time mtime_;
+
+  // The name of the encryption key used to encrypt this item on the server.
+  // Empty when no encryption is in use.
+  std::string encryption_key_name_;
 };
 
 }  // namespace syncer