Revert of [DevTools] Don't handle shortcuts while dialog is open. (https://codereview.chromium.org/214453003/)

Reason for revert:
We should still intercept browser shortcuts, even with dialog open.

Original issue's description:
> [DevTools] Don't handle shortcuts while dialog is open.
> 
> BUG=356616
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170294

TBR=apavlov@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=356616

Review URL: https://codereview.chromium.org/219013004

git-svn-id: svn://svn.chromium.org/blink/trunk@170436 bbb929c8-8fbe-4397-9dbb-9b2b20218538