Fix another batch of leaks in the Blink unit tests.

With this, we go from 306248 bytes leaked in 576 allocations to 21192
bytes leaked in 94 allocations.

BUG=none
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/180223003

git-svn-id: svn://svn.chromium.org/blink/trunk@167831 bbb929c8-8fbe-4397-9dbb-9b2b20218538