.gitignore some generated XCode project files.

BUG=297962

Review URL: https://chromiumcodereview.appspot.com/24488003

git-svn-id: svn://svn.chromium.org/blink/trunk@158310 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make dialog::backdrop span the viewport by default.

As per the recent spec change: http://html5.org/r/8197

No new test, covered by modifying modal-dialog-backdrop.html
Existing tests that don't test backdrop specifically are
modified to have display: none backdrops.

BUG=140205

Review URL: https://chromiumcodereview.appspot.com/24493004

git-svn-id: svn://svn.chromium.org/blink/trunk@158311 bbb929c8-8fbe-4397-9dbb-9b2b20218538