GitLab

NativeScrollBar used to wrap NativeScrollBarViews, but it was almost
entirely a pass-through shim. Thus, now we just have one layer of views
scrollbars called ScrollBarViews.

BUG=662605

Review-Url: https://codereview.chromium.org/2480763005
Cr-Commit-Position: refs/heads/master@{#430316}