Set detached wallpaper on the scale up animation.

This keeps the background wallpaper from disappearing when expanding an
app that has a wallpaper background (e.g. clock).

Fixes bug 6649988. The second half of the bug, the first half will be
reissued as a new bug.

Change-Id: I209c9038469e4133586a927c92ef64ae43fb937f

services/java/com/android/server/wm/WindowManagerService.java

@@ -1740,8 +1740,6 @@ public class WindowManagerService extends IWindowManager.Stub
                             mWallpaperTarget = oldW;
                             foundW = oldW;
                             foundI = oldI;
-                            mLowerWallpaperTarget = null;
-                            mUpperWallpaperTarget = null;
                         } 
                         // Now set the upper and lower wallpaper targets
                         // correctly, and make sure that we are positioning
@@ -3162,6 +3160,7 @@ public class WindowManagerService extends IWindowManager.Stub
             set.addAnimation(scale);
             alpha.setDuration(duration);
             set.addAnimation(alpha);
+            set.setDetachWallpaper(true);
             a = set;
         } else {
             a = createExitAnimationLocked(transit, duration);