Screen rotation animation implementation has been changed to optimize the performance.

There is a test in OverviewButtonTrayTest, to test the screen rotation animation will not interrupt the hide animation of OverviewButtonTray.
Since the new implementation will be co-exist with the old implementation, we need to add more tests to cover both situations. Because the new implementation is asynchronous and the screen_rotation_animator_unittest already adds the hooks to waiting for the callbacks, therefore it would be easier to test the interactions in screen_rotation_animator_unittest.cc.

1) Add two tests in screen_rotation_animator_unittest
2) Also change one of OverviewButtonTrayTest, to test hide animation will not interact with explicitly deleting layers, not through ScreenRotationAnimation.