Split reflection out of RenderLayer.

This moves the reflection methods out of RenderLayer and into a RenderLayerReflectionInfo
class.

BUG=260898

Review URL: https://codereview.chromium.org/40413002

git-svn-id: svn://svn.chromium.org/blink/trunk@160685 bbb929c8-8fbe-4397-9dbb-9b2b20218538