MD Bookmarks: Disable keyboard shortcuts when a dialog is open

Even though our dialogs are modal, it was still possible to execute
keyboard commands on the background content by clicking on the dialog
background, which refocuses the document body and allowed commands
to execute.

Bug: 742972
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I01f9cb3060fd6a91a6fa5a832578f3f245712e0c
Reviewed-on: https://chromium-review.googlesource.com/575252
Reviewed-by: calamity <[email protected]>
Commit-Queue: Tim Sergeant <[email protected]>
Cr-Commit-Position: refs/heads/master@{#488116}
3 files changed