Minor cosmetic cleanup in FrameView

Micro cleanup of awkward nested 'if statement' in FrameView::layout().

BUG=

Review URL: https://codereview.chromium.org/177003021

git-svn-id: svn://svn.chromium.org/blink/trunk@168158 bbb929c8-8fbe-4397-9dbb-9b2b20218538