Chrome Version: 51.0.2671.0 (Official Build) fcf7354b33a5df1f26cee7c2da9b7c4864897679-refs/heads/master@{#379691}
OS: Mac
 
Pre-condition: Enabled 'Media Router' flag from chrome://flags

Steps:
1. Launch Chrome and go to NTP.
2. Right click to open the context menu and select 'Cast' 
3. Right click on 'Cast' overlay and select 'View Page Source' option from context menu(opened in New tab).
4. Observe cast overlay on previous tab.

Actual: Cast overlay get close after opening 'View Page Source' tab 

Expected: Cast overlay should not get close after opening 'View Page Source' tab 

This is a regression issue broken in M-51, below is bisect info

Good Build: 51.0.26670.0
Bad Build: 51.0.26671.0

Narrow Bisect:
https://chromium.googlesource.com/chromium/src/+log/7e6264ce0f355de7894f8bbc525b55cd85ccfbb9..c55bcebd87beeef0bf808a8fab7d2e57d36e4809?pretty=fuller&n=100

Suspecting: r379659

Note: Issue is not seen on Windows and Linux OS.