Group bookmark modifications into a single undo action.

The following user actions in the bookmark manager cause multiple
changes to the BookmarkModel. They are now grouped into a single undo
action.
1) Select multiple bookmarks and/or folders and "Cut".
2) Drag multiple bookmarks and/or folders and drop somewhere else in
the bmm.
3) Drag multiple bookmarks and/or folders from one profile to the bmm
of a different profile.
4) Paste multiple bookmarks.
5) Select multiple bookmarks and delete.
Note: Bookmarks here can refer to

BUG=126092

Review URL: https://codereview.chromium.org/100013004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241973 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241973