Avoid Showing rotation change notification when source is accelerometer

BUG=717252
TEST=Manually rotate device with accelerometer and observe there's no notification

Review-Url: https://codereview.chromium.org/2853113005
Cr-Commit-Position: refs/heads/master@{#469058}
ScreenLayoutObserverTest::ScreenLayoutObserverTest() {}

ScreenLayoutObserverTest::ScreenLayoutObserverTest() {}
