I have faced the problem described in this question
How to debug Javascript in Chrome on a Visualforce page?
earlier opening dev tools before opening visual force (or clearing the cache) page resolved the problem in the past.
However since August 8th 2016: 1) I can NOT see the code as shown in the screenshot above. 2) The console.log commands in my javascript from my Visualforce page work 3) Any functions I call from the command line do not work. 4) There are no exceptions thrown when I type any commands even no "Uncaught ReferenceError:" This is happening only for visualforce page iframe and not the TOP frame.
My environment: Windows 8.1, Chrome 52.0.2743.116 m (64-bit)
Does anyone know how to fix this?