Clean up netinfo layout tests

Use shouldBe instead of conditionals, also removed a redundant check from multiple-frames.html

BUG=

Review URL: https://codereview.chromium.org/312753002

git-svn-id: svn://svn.chromium.org/blink/trunk@175385 bbb929c8-8fbe-4397-9dbb-9b2b20218538