GitLab

- Add the tab strip height factor into the transition equation to make sure the
transition is anchored to the top of the tab.
- Override ntp_search_box_transition_length to make the transition take longer
on tablets.

BUG=625145

Review-Url: https://codereview.chromium.org/2345673002
Cr-Commit-Position: refs/heads/master@{#419137}