• New non-backwards compatible API.
  Use Platform.current to access the current platform,
  and Platform.current.nativePlatform to either get access to native
  platform information, or get a null on non-native platforms.
  Similarly Platform.current.browserPlatform is only non-null on the web.
  Mocking APIs are moved to a separate library to ensure they are
  only used for testing, and to allow better performance in production.
  Legacy APIs are deprecated, but retained and emulated using the new API.
  Use dart fix to migrate off the deprecated API.