Accept in_reply_to to thread inline comments

The in_reply_to field supplies the id of another comment, enabling
threading. Because id is URL encoded to match a REST API we also
encode the in_reply_to field, allowing clients to correctly line up
messages by simple string equality.

Change-Id: Idc6af51873b9b8a12707c6f4df9d25b627e8b409

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/PatchLineComment.java

@@ -185,4 +185,8 @@ public final class PatchLineComment {
   public String getParentUuid() {
     return parentUuid;
   }
+
+  public void setParentUuid(String inReplyTo) {
+    parentUuid = inReplyTo;
+  }
 }