Thanks for filing the issue!

@Reporter: Could you please share a sample test file/URL which helps us to triage the issue in a better way. Any further inputs from you end may help.

It seems to have to do if running on localhost or not. 

- If I run a simple console.log(screen.width) (see my test.html) on localhost in the emulator (Galaxy S5) the console.log returns the 1920 px of my pc
- If I run the same script on the server in the emulator (Galaxy S5) the console.log returns the 360 px of the emulated device, as expected
- If I call my localhost via the local ip in our network the behavior is like on the server (360 px)

So the problem seems to exist if using the emulator on localhost (as most dev environments). Thanks for looking into it!

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Checked the issue on reported chrome version 64.0.3282.167 and on the latest canary 65.0.3350.0 as per the feedback given in comment#3 by reporter with the below mentioned steps.
1. Launched Chrome
2. Opened DevTools->Toggle Device
3. Selected Galaxy S5
4. Given command console.log(screen.width)
We observed the screen resolution of the PC initially, then after running the command "console.log(screen.width)" we got the resolution of the device. Attaching the screen shot of the same.

@Reporter: Could you please clarify us on, whether getting the information about PC initially is the issue or even after running the given command in console you are getting the PC info instead of Galaxy S5 info ?. Any further inputs from your end may help us, Providing with the screen shot/screen cast would serve us better in understanding it.

Thanks!

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Thanks for testing!

I also retested and my assumption that it has to do with localhost seems to be wrong.

One time I open my local test file and run additional console.logs which return the screen width of the PC (1920px), another time the same setup returns the screen width of the emulated device (360px). (See my screenshots). 
I can not reproduce the problem systematically myself, but I regularly see it in development now using the emulator.

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@Reporter: From your comment#6 it is understood that the issue is not seen consistently, could you please check the same in a new profile and let us know if the issue is still seen without any apps and extensions i.e., in a fresh profile/new person.

Thanks!

Closing as non-reproducible. If you manage to repro it, please reopen.