The debug agent sets a breakpoint in Thread.resume() so it can prevent the debugger from suspending threads while in the resume call:

             /*
              * Track the resuming thread by marking it as being within
              * a resume and by setting up for notification on
              * a frame pop or exception. We won't allow the debugger
              * to suspend threads while any thread is within a
              * call to resume. This (along with the block below)
              * ensures that when the debugger
              * suspends a thread it will remain suspended.
              */
             trackAppResume(resumer);

Now that Thread.resume() is unsupported and just throws UnsupportedOperationException, all debug agent code related to this support can be removed. It's at least a couple of hundred lines of code, and with a fair amount of confusing synchronization. It will be nice to see it go.

For removal, search for code that references "AppResume" (do a case insensitive search). That should catch everything. I believe it is all contained to threadControl.c