Implement Media Galleries scan result dialog for Mac.

Depends on https://codereview.chromium.org/148093011/
Known Issues:
Attached text does not elide.
Open in folder pops under

BUG=161119

Review URL: https://codereview.chromium.org/131103024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248300 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248300