Mark slow tests as slow.

TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/755283004

Cr-Commit-Position: refs/heads/master@{#25511}
Double timeout for slow tests.

TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/752733003

Cr-Commit-Position: refs/heads/master@{#25512}