Properly interpret orientation provider/listener test results.

This change makes sure orientation test results are properly interpreted
for devices which natural orientation is landscape.

Existing implementation assumed portrait as device natural orientation.

BUG=
TEST=Run ContentShell instrumentation test.
./build/android/test_runner.py instrumentation --test-apk=ContentShellTest --release --test-filter=ScreenOrientation*

Review URL: https://codereview.chromium.org/608503003

Cr-Commit-Position: refs/heads/master@{#297670}