Move ViewDisplayList to GraphicsLayer

This CL moves ViewDisplayList to GraphicsLayer and renames it to
DisplayItemList.

DisplayItemList and the DisplayItems are also moved to platform/graphics
to resolve layering violation. The recorders stay in core/paint.

Review URL: https://codereview.chromium.org/702633002

git-svn-id: svn://svn.chromium.org/blink/trunk@185263 bbb929c8-8fbe-4397-9dbb-9b2b20218538