If we navigate to an existing, named frame in a different page, focus the page.

BUG=286018
TEST=WebViewTest.FocusExistingFrameOnNavigate

Review URL: https://chromiumcodereview.appspot.com/23981011

git-svn-id: svn://svn.chromium.org/blink/trunk@157613 bbb929c8-8fbe-4397-9dbb-9b2b20218538