Only allow focused window to select seamless rotation.

We require apps to opt in to seamless rotation. If a dialog or some such
has popped up above them, the dialog may not be prepared to rotate
seamlessly and we should just fall back to the old behavior for now.

Bug: 30968345
Change-Id: Ib9a7352ed84d41076bdd162bf38d151b053a307e

services/core/java/com/android/server/policy/PhoneWindowManager.java

@@ -7756,6 +7756,9 @@ public class PhoneWindowManager implements WindowManagerPolicy {
         }
 
         final WindowState w = mTopFullscreenOpaqueWindowState;
+        if (w != mFocusedWindow) {
+            return false;
+        }
 
         // We only enable seamless rotation if the top window has requested
         // it and is in the fullscreen opaque state. Seamless rotation