Add LwwRegister CRDT

blimp/common/proto/helium.proto

Index: blimp/common/proto/helium.proto
diff --git a/blimp/common/proto/helium.proto b/blimp/common/proto/helium.proto
index 774560ecb053abc9dbacaa7266c88bfeec1f26e4..23e77cb1eaf586c7b16d66f8f984d4a49ca29003 100644
--- a/blimp/common/proto/helium.proto
+++ b/blimp/common/proto/helium.proto
@@ -25,12 +25,20 @@ message TestChangesetMessage {
   int32 value2 = 2;
 }
 
+message LwwRegisterChangesetMessage {
+  oneof register {
+    int32 integer_value = 1;
+    string string_value = 2;
+  }
+}
+
 // A union of serializable Changeset types. There will be one for each Helium
 // Object that requires serialization.
 message ChangesetMessage {
   oneof payload {
     // Sample message for the test
     TestChangesetMessage test = 1;
+    LwwRegisterChangesetMessage lww_register = 2;
   };
 }