The chart for participant logs is not displaying at the top of the participant logs report.

Replication steps:

1. Log in as an administrator or teacher
2. Go to a course that has students enrolled
3. Go to the participants page and pick one user
4. In the administration block, select the All logs activity report (Profile for picked user -> Activity Reports -> All logs)
5. Check that a chart image appears above the table of activity.
6. repeat for Today's logs

Here's a breakdown of the display/not display of the Chart for Participant logs.

1.- On my online moodle test site running PHP Version 5.3.16 the Chart image is displayed as expected in moodle 2.4.

2.- On my local moodle test site running PHP Version 5.4.7
2a.- the Chart image is correctly displayed in moodle 1.9 and moodle 2.1
2b.- the Chart image is NOT displayed in moodle 2.2, 2.3, 2.4 and moodle 2.5 (dev).

This seems to be a known issue, sometimes marked as resolved in the tracker, and sometimes not.

See e.g. https://github.com/PukunuiAustralia/moodle-courseformat_grid/pull/12