The problem is that OOBE has a fixed-size window which probably doesn't respect the display's workarea (which the docked magnifier changes). alemate@ can you please take a look?

I don't know how magnifier is expected to work.

Could you suggest what we could change here?

Expected: I recommend to view the Email text field at least when entering some text
Actual:Unable to view the Email field when editing.

Magnifier changes the display's workarea [1] in the same way the shelf, and the chromevox panel do. Effectively reducing the height of the available area for windows. Windows should respect that, so instead of basing your window size on the full size of the display, you can base it on the workarea size. You can use the WorkAreaWatcherObserver [2].

[1]: https://cs.chromium.org/chromium/src/ui/display/display.h?type=cs&q=display::Display::work_area&l=120

[2]: https://cs.chromium.org/chromium/src/ui/base/work_area_watcher_observer.h?type=cs&q=Workareachange&l=17

 Issue 875949  has been merged into this issue.

This is now the master bug for these issues across the UI. Relevant bugs that aren't merged yet, please consider merging: 
868625
868623
865795
865792

The old title is wrong. Docked magnifier changes the workarea, some other system components don't respect the modified workarea

Thanks for that update and clarification, afakhry@. Please let me know if you feel that all these bugs should be merged as dupes. Otherwise, I'll just leave this as the master blocking bug. 

Jacob, could you help finding owner for this?

alemate@ this should be easy to fix for OOBE, just listen to display::DisplayObserver::OnDisplayMetricsChanged() for DISPLAY_METRIC_WORK_AREA and update your bounds according to the current display's Display::work_area().