Page::settings() should return a reference.

It's never null. We remove some unnecessary null check for it.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23075005

git-svn-id: svn://svn.chromium.org/blink/trunk@156196 bbb929c8-8fbe-4397-9dbb-9b2b20218538