Support executing named commands on IDC_BOOKMARK_PAGE when overriding the bookmark shortcut

Implements the "Bookmark this page..." menu override for
named extension commands, from the Remove Bookmark Shortcut Chrome API proposal:
https://docs.google.com/a/chromium.org/document/d/1C2Mle92O9uGlji5y5gGDM5tNJ_tVE1Vb-2xgsZPNDTk

BUG=335655

Review URL: https://codereview.chromium.org/181503010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254226 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254226