pointer: Merge pointer.js into message_scroll.js.

Ths remaining code here is naturally message scrolling logic, and fits
well into the existing file for handling that.

static/js/message_scroll.js

@@ -158,6 +158,26 @@ exports.initialize = function () {
         unread_ops.process_visible();
         scroll_finish();
     }, 50));
+
+    // Scroll handler that marks messages as read when you scroll past them.
+    $(document).on('message_selected.zulip', function (event) {
+        if (event.id === -1) {
+            return;
+        }
+
+        if (event.mark_read && event.previously_selected !== -1) {
+            // Mark messages between old pointer and new pointer as read
+            let messages;
+            if (event.id < event.previously_selected) {
+                messages = event.msg_list.message_range(event.id, event.previously_selected);
+            } else {
+                messages = event.msg_list.message_range(event.previously_selected, event.id);
+            }
+            if (event.msg_list.can_mark_messages_read()) {
+                unread_ops.notify_server_messages_read(messages, {from: 'pointer'});
+            }
+        }
+    });
 };