Viewport should zoom out when screen magnification is disabled.

1. If screen magnification is disabled when the screen is in a
   magnified state we have to zoom out since otherwise the user
   is stuck in a magnified state without ability to pan/zoom/
   toggle magnification which renders the device useless.

bug:7131030

Change-Id: I8f3339f31310448ec8742f3101c1fdc61a6a5f83

services/java/com/android/server/accessibility/ScreenMagnifier.java

@@ -245,6 +245,7 @@ public final class ScreenMagnifier implements EventStreamTransformation {
     public void onDestroy() {
         mMagnificationController.setScaleAndMagnifiedRegionCenter(1.0f,
                 0, 0, true);
+        mViewport.setFrameShown(false, true);
         mDisplayProvider.destroy();
         mDisplayContentObserver.destroy();
     }