Update DimAnimator layer when its window changes.

Prior to this fix once dimming had been turned on it stayed at the
same layer and associated with the same window until it was turned
off. Now the DimAnimator layer is updated if either the window layer
changes or the dimming window changes.

Fixes bug 6467865.

Change-Id: I3e1765b92b51be26e3718c8a87e2583041a36af9
diff --git a/services/java/com/android/server/wm/WindowAnimator.java b/services/java/com/android/server/wm/WindowAnimator.java
index 5536559..bc84d3c 100644
--- a/services/java/com/android/server/wm/WindowAnimator.java
+++ b/services/java/com/android/server/wm/WindowAnimator.java
@@ -548,6 +548,10 @@
         return mDimParams != null;
     }
 
+    boolean isDimming(final WindowStateAnimator winAnimator) {
+        return mDimParams != null && mDimParams.mDimWinAnimator == winAnimator;
+    }
+
     public void dump(PrintWriter pw, String prefix, boolean dumpAll) {
         if (mWindowDetachedWallpaper != null) {
             pw.print("  mWindowDetachedWallpaper="); pw.println(mWindowDetachedWallpaper);