Media Galleries: Add missing include from r230593.

R=rsleevi@chromium.org
TBR=gbillock@chromium.org

Review URL: https://codereview.chromium.org/39103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230598 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230598