Remove cached bounds in RenderLayer.

This removes m_location, m_size, and m_offsetForInFlowPosition from RenderLayer, as well as the expensive layer tree walk that updates these fields during overflow scrolls.

BUG=400589

Review URL: https://codereview.chromium.org/445263002

git-svn-id: svn://svn.chromium.org/blink/trunk@179768 bbb929c8-8fbe-4397-9dbb-9b2b20218538