Revert "Move RoundedRect from core/platform/graphics to platform/geometry"

This reverts https://src.chromium.org/viewvc/blink?revision=158824&view=revision which broke win canary build

TBR=eae
BUG=297477

Review URL: https://codereview.chromium.org/25629004

git-svn-id: svn://svn.chromium.org/blink/trunk@158826 bbb929c8-8fbe-4397-9dbb-9b2b20218538