Oilpan: fix build after r363998.

The struct contains a raw pointer to an Oilpan heap object (Scrollbar*),
which is not allowed without either accounting for its safety (or
by having it be traced.)

But as the struct is unused, just remove it.

R=haraken
BUG=560418
NOTRY=true

Review URL: https://codereview.chromium.org/1515503002

Cr-Commit-Position: refs/heads/master@{#364015}
1 file changed