See attachment. 
- On the left is our device mode, viewing the site
- on the right, is a frame from disabled-by-default-devtools.screenshot while page is under  Emulation.setDeviceMetricsOverride

Looking over at https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/devtools/devtools_frame_trace_recorder.cc&q=%22devtools.screenshot%22&sq=package:chromium&type=cs&l=78

We are setting the size of the image to scrollable_viewport_size, but this doesn't account for any active emulation, and instead looks at overall desktop window size. dgozman identified that a separate property (which?) should have our correct viewport size.

caseq, can you look at this? 
 

Deleted: Screen Shot 2016-05-13 at 10.45.37 AM.png 96.3 KB

	Screen Shot 2016-05-13 at 10.45.37 AM.png 96.3 KB View Download