Add depth animation when multiwindow mode changes.

This is a workaround until we can support app transitions when starting
an activity in mw mode.

Bug: 158613217
Change-Id: I843d6669722c543728ab532e1c4fbd4643f6f135

quickstep/src/com/android/launcher3/BaseQuickstepLauncher.java

@@ -83,6 +83,7 @@ public abstract class BaseQuickstepLauncher extends Launcher
         super.onCreate(savedInstanceState);
 
         SysUINavigationMode.INSTANCE.get(this).addModeChangeListener(this);
+        addMultiWindowModeChangedListener(mDepthController);
     }
 
     @Override