Able to reproduce on Windows-10 Dell Precision M3800(HiDpi) using chrome latest stable M59-59.0.3071.115. 

Bisect Information:
--------------------
Good build: 54.0.2794.0 
Bad Build : 54.0.2795.0 

You are probably looking for a change made after 404867 (known good), but no later than 404885 (first known bad).

Change Log URL: 
https://chromium.googlesource.com/chromium/src/+log/af2f49ba57ed217d06e69830f325c9ba7e7ce0bd..57b70dae30c2bc7d60e70efd8ebae83e01fe9119

From the above change log suspecting below change
https://chromium.googlesource.com/chromium/src/+/56aad7e3f2b8d6837cc163b08e4bc63dd189ab00

enne@ - Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner. Adding RB-stable for M-60 please feel free to edit if this is not the case.

Thanks!

Could you please provide update on this? 
Thanks. 

This seems much more likely to be bsep's https://chromium.googlesource.com/chromium/src/+/f449a7f4828a5610b1e21b8d2e378555fa59ca7b change

I don't have a Windows machine handy at the moment.  bsep, can you repro this more easily?

I think everything here is working as intended... I can't tell what you expect to happen or what the bisect was looking for. I disabled Use Zoom For DSF just to make sure, and the content is exactly the same size, albeit much blurrier.

Your content is 500 CSS pixels wide, which is what was declared. On my 150% scaling machine the box is 750 physical pixels wide, which is... 150% as big. In the screenshot you posted it is 1000 physical pixels wide, which is what I would expect from a 200% machine. The extensions UI is not, and shouldn't be, exempt from scaling.

As far as the height goes, you're using a <p> tag, which adds a margin above and below your text, which is why there's extra space there.

DPI scaling is using more physical pixels to display the same content, so 500 CSS pixels will use 1000 physical pixels to display (in the case of 200% scaling), and not add 500 white pixels to the left. 

Surface Pro 4 have 2736 physical pixels across, the 500 CSS pixels options UI is taking well over half the screen to display, it looks like it is taking 2000 physical pixels. 

Chromium should look the same across all devices right? How is it working as intended when it looks like [ http://i.imgur.com/ce0KVEJ.png ] on my PC but [ http://i.imgur.com/4zlvtOp.png ] on my tablet? 

Oh! I'm sorry, you are right, that is a bug. I didn't notice it in your screenshot because it had already been fixed and did not reproduce for me. Please look forward to it in M61.

Marking as duplicate.