Not showing Test code coverage on developer console

Go to the 'Apex Test Execution'and in option select list deselect the 'Store Only Aggregated Code Coverage' checkbox.

It appears that in latest Winter 2016 upgrade a bug was introduced where code coverage line highlights are missing from the Salesforce Developer Console

You can get them back by selecting the 'Test > Always Run Asynchronously' checkbox and re-running your test.