Update popup blocker behavior and tests

The tests now also check whether a background or foreground tab is
opened. We also make the behavior of the popup blocker match the
behavior of the render view (which is to not mess with the disposition)

BUG=431335
R=mkwst@chromium.org

Review URL: https://codereview.chromium.org/731083002

Cr-Commit-Position: refs/heads/master@{#304593}
2 files changed