[Files.app Gallery] Prevent the placeholder from being visible in the message

BUG=344269
TEST=manually tested

Review URL: https://codereview.chromium.org/182543004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253783 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253783