Unable to set breakpoints in Chrome dev tools, version 26.0.1410.64 m
clicking on the De-Obfuscate Source button (i.e. {}) solved this issue for me.
I'm a fool! haha! breakpoints are set in the Source pane )))
It's been a while, but in version 33.0.1750.146, but my problem was that I was on the Sources pane (I'd call this a tab; it's one of the items at the very top of the window), but I was on the Content scripts tab (on the left hand side). I needed to switch to the Sources tab.
To be clear, there are two sets of Sources tabs; one is within the other.
UPDATE 2016-01-07: Now I'm on 47.0.2526.106. The only thing that worked for me today was to close DevTools and re-open. It was a little finicky. It worked once, then stopped, and I had to close the DevTools and re-open again. I saw @johntrepreneur's answer about closing the browser, but unfortunately I have too many tabs open on too many workspaces, so that's too much of a pain, so I didn't try that, although I have to assume that would work.