Hi, if you are using maven based project, you can just enter ComponentControlHandler class and sources should be attached automatically to debugger.
Otherwise, you may download them and attach manually.
What I'm usually doing is checking ource on GitHub, for this case:
GitHub has very nice user interface for working with types - how I have found the ComponentControlHandler.java:96?
Press "T" and type "ComponentControlHandler"
Select the "ComponentControlHandler.java" in the list of listed files
Open "L" and type "96"
Cool. Many thanks, Lukáš