Move platform/graphics/chromium/* to platform/graphics/

BUG=303332
R=abarth@chromium.org, schenney@chromium.org

Review URL: https://codereview.chromium.org/26679003

git-svn-id: svn://svn.chromium.org/blink/trunk@162052 bbb929c8-8fbe-4397-9dbb-9b2b20218538