sensor-tester: orientation locking does not always work

Spun off #66. Some screen locking combinations in tests such as "Accelerometer with screen coordinates" don't work: for example, locking to 180 degrees then 90 while originally in portrait mode causes the latter to fail and reset the orientation locking mechanism.

There's also additional information in #66 written by @kenchris.

We need to figure out if we're doing something wrong or whether we're hitting one or more Chromium bugs.