Chrome Version: 54.0.2799.0 (Official Build)8acb9d5f2f71c3df8e64b13ee321a9d194e89785-refs/heads/master@{#405947} 32/64-bit.
OS: Windows (7,8,10) [Resolution: 1366 x 768]

Steps: 
1. Launch chrome and navigate to chrome://settings, click on 'Show advanced settings...'
2. Hit Ctrl+Shift+I to open devtools and 'dock it to right'.
3. Toggle to device mode, select 'iPhone 6' and scroll the page.
4. Click the toggle device mode button twice and observe the page.

Actual: Page appear weird in device mode (i.e. unwanted gray patch is observed).

Expected: Page should be properly seen.

This is a regression issue broken in M-53.

Manual Regression Range:
Good Build: 53.0.2774.0 
Bad Build: 53.0.2775.0 

Narrow Bisect:
https://chromium.googlesource.com/chromium/src/+log/09d68138f934a472dedb9b321e2cef88e9279806..151d5d907870e262ff7f94fd4b1f1e5ef887e96d?pretty=fuller&n=100

Suspecting: r400767 ?

Please re-assign if your change is not the cause of this issue.

Note: 1. Issue is not seen in Mac and linux OS.
2.Issue is resolution specific, only reproducible in 1366 x 768. 
 

Deleted: Actual.mp4 860 KB

	Actual.mp4 860 KB View Download

Deleted: Expected.mp4 781 KB

	Expected.mp4 781 KB View Download