Fixed improperly rendered error messages in gallery in Files.app.

Error messages were black on almost black background. The color has been changed to white.

TEST=Invoke an error message by eg. opening a broken image file (eg. empty jpg file).
BUG=168041


Review URL: https://chromiumcodereview.appspot.com/11833026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176081 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/css/gallery.css

@@ -1055,6 +1055,7 @@ body {
     url('../images/media/2x/error.png') 2x);
   background-position: 25px center;
   background-repeat: no-repeat;
+  color: white;
   display: -webkit-box;
   height: 54px;
   padding-left: 70px;