Remove redendant frameViewDidScroll call.

frameViewDidChangeSize calls it if m_containerLayer and
m_containerLayer is always non-null in this location.

Also, remove a redundant "private" from RenderLayerCompositor.h.

Review URL: https://codereview.chromium.org/239393004

git-svn-id: svn://svn.chromium.org/blink/trunk@171699 bbb929c8-8fbe-4397-9dbb-9b2b20218538