unread_ops: Add function to mark PM threads as read.

This will be used recent topics to mark PM rows as read.

frontend_tests/node_tests/message_flags.js

@@ -256,6 +256,17 @@ run_test("read", ({override}) => {
         },
         success: channel_post_opts.success,
     });
+
+    msgs_to_flag_read = [1, 2, 3, 4, 5];
+    message_flags.mark_as_read(msgs_to_flag_read);
+    assert.deepEqual(channel_post_opts, {
+        url: "/json/messages/flags",
+        data: {
+            messages: "[1,2,3,4,5]",
+            op: "add",
+            flag: "read",
+        },
+    });
 });
 
 run_test("read_empty_data", ({override}) => {

static/js/message_flags.js

@@ -66,6 +66,10 @@ export const send_read = (function () {
     return add;
 })();
 
+export function mark_as_read(message_ids) {
+    send_flag_update_for_messages(message_ids, "read", "add");
+}
+
 export function mark_as_unread(message_ids) {
     send_flag_update_for_messages(message_ids, "read", "remove");
 }

static/js/unread_ops.js

@@ -227,3 +227,11 @@ export function mark_topic_as_read(stream_id, topic, cont) {
         success: cont,
     });
 }
+
+export function mark_pm_as_read(user_ids_string) {
+    // user_ids_string is a stringified list of user ids which are
+    // participants in the conversation other than the current
+    // user. Eg: "123,124" or "123"
+    const unread_msg_ids = unread.get_msg_ids_for_user_ids_string(user_ids_string);
+    message_flags.mark_as_read(unread_msg_ids);
+}