GitLab

The "loading..." shield on OSX had the currently focused UI element
"shine through" - i.e. the entire dialog was hidden behind it except
for the one focused element.

This change makes the loading screen first responder for the duration
of its visibility, preventing focus rings.

R=sail@chromium.org
BUG=none

Review URL: https://chromiumcodereview.appspot.com/23477044

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221862 0039d316-1c4b-4281-b951-d872f2087c98