Also ensure that the top-margin between the first card and the toolbar is same as in the list view.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5cb5dadf856d314cfe85259b1b23d2985defbf69

commit 5cb5dadf856d314cfe85259b1b23d2985defbf69
Author: Dan Beam <dbeam@chromium.org>
Date: Tue Nov 28 05:49:00 2017

MD Extensions: remove section header from shortcuts view

It's duplicative with input validation messaging and this was requested
by designer bettes@ during a polish pass.

Bug:  787227 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1e9f3267b8a62f886ebb0b6ff93d59f6d1006aa2
Reviewed-on: https://chromium-review.googlesource.com/786398
Commit-Queue: Dan Beam (no longer on Chrome) <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519585}
[modify] https://crrev.com/5cb5dadf856d314cfe85259b1b23d2985defbf69/chrome/app/md_extensions_strings.grdp
[modify] https://crrev.com/5cb5dadf856d314cfe85259b1b23d2985defbf69/chrome/browser/resources/md_extensions/keyboard_shortcuts.html
[modify] https://crrev.com/5cb5dadf856d314cfe85259b1b23d2985defbf69/chrome/browser/ui/webui/extensions/extensions_ui.cc