[Temp] Backport r290626 from Chromium.

This is necessary for our Ozone-Wayland builds, and corresponds to its
patches/0006-Backport-481073003.patch.

Original commit message:

  Have WTH call cursor function in platform_window directly

  WTH now calls into platform_window for cursor updates. This also means that
  there are no public callers for EventFactoryOzone, so removing it from the
  Ozone interface.

  BUG=392280
  NOTRY=true

  Review URL: https://codereview.chromium.org/481073003