I'm using Chrome developer tools for version 49.0.2623.110 m and I notice that the little box displaying the window WIDTHxHEIGHT when you resize is now gone or moved. Am I just not seeing it? Is it moved?
I use Viewport Resizer now but I really missed having both options to check window size...
I was looking for answers to this problem myself, and I found a couple of pages. Apparently, it's a bug in Chrome v49, that should be fixed in Chrome 50. Here are a couple of links to the discussions:
https://productforums.google.com/forum/#!topic/chrome/LhOfBFSBdx8
https://bugs.chromium.org/p/chromium/issues/detail?id=582421