Reapply "Media Galleries API: Fix MediaGalleriesPreferences initialization for fresh profiles."

This is a reapplication 25539003.

Previous patch broke unit_tests because a conditional was inverted.

TBR=vandebo
BUG=151701, 295880

Review URL: https://codereview.chromium.org/25780002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226616 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226616
Makes RecentlyUsedFoldersComboModel clear internal structur when node deleted

Prior to this RecentlyUsedFoldersComboModel would not clear its
internal structures if a node was deleted, leading to a future
crash. This patch makes RecentlyUsedFoldersComboModel clear internal
structure and notify observers.

Having the BookmarkModel change while the bubble is showing is rare,
so the code doesn't attempt to do anything elegant.

BUG=294330
TEST=none
R=msw@chromium.org

Review URL: https://codereview.chromium.org/25310003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226618 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226618