Use launcher surface when removing launch target

Otherwise events won't be dispatched properly and window opacity will be
wrong.

Test: manual
Fixes: 191149025
Change-Id: Ice7ea86252282c7dc1cb5925dd1bdb8cade89c08

quickstep/src/com/android/launcher3/statehandlers/DepthController.java

@@ -180,6 +180,12 @@ public class DepthController implements StateHandler<LauncherState>,
      * Sets the specified app target surface to apply the blur to.
      */
     public void setSurface(SurfaceControl surface) {
+        // Set launcher as the SurfaceControl when we don't need an external target anymore.
+        if (surface == null) {
+            ViewRootImpl viewRootImpl = mLauncher.getDragLayer().getViewRootImpl();
+            surface = viewRootImpl != null ? viewRootImpl.getSurfaceControl() : null;
+        }
+
         if (mSurface != surface) {
             mSurface = surface;
             if (surface != null) {