AI 147976: Compatibility mode support. Part 2.

  * Introduced ApplicationScale (may not be good name. CompatibilityScale? CanvasScale? Pls let me know if you have better idea)
  * Changes to RootView / SurfaceView
  - Makes the app believe it's running in the supported density/resolution.
  - Makes the window manager believe it's running at the right density/resolution.
  * Added methods to Rect/Event for scaling up/down.
  Known issues:
  * certain kind of images (such as nine patch for buttons) seesm to be loaded not by app, thus does not take the scale into account,
  which, in turn, is causing layout issue.
  * ZoomButton in MapView is rendered in wrong place
  * Transparent region on Surface is not correct
  * Specifying different densities in one process is not working.
  BUG=1770627

Automated import of CL 147976