mash: Activation and Z-ordering broken around chrome app menu

On ToT @ #501046:
(1) run chrome --mash (browser window A should be in foreground)
(2) make a new chrome window with Ctrl+N (window B now in foreground)
(3) click the app menu button on window A (now in the background)
Expected: Window A should be brought to the foreground.
Actual: Window A shows a menu but remains in the background

This may be related to  Issue 730890 .
Scott, lmk if you want me to take a look.
 

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