Don't create new nav bar layer when IME is rendering nav buttons

Test: Edit folder name in taskbar, ensure we don't create a new window
Fixes: 214571910
Change-Id: I9a1385dbed2df7a4ee141485c8bbfb521457d853

quickstep/src/com/android/launcher3/taskbar/TaskbarActivityContext.java

@@ -240,6 +240,10 @@ public class TaskbarActivityContext extends ContextThemeWrapper implements Activ
         return mNavMode == Mode.THREE_BUTTONS;
     }
 
+    public boolean isGestureNav() {
+        return mNavMode == Mode.NO_BUTTON;
+    }
+
     public int getLeftCornerRadius() {
         return mLeftCorner == null ? 0 : mLeftCorner.getRadius();
     }