Animate the dock divider appearance/disappearance.

We want to animate the dock divider appearance only after the entrance
animation of the docked activity finishes, so these two don't clash. For
disappearance they will animate together.

Bug: 24913915
Change-Id: Ibe5c3960f21fcc5e64039b158605fa09017c5c34
diff --git a/services/core/java/com/android/server/policy/PhoneWindowManager.java b/services/core/java/com/android/server/policy/PhoneWindowManager.java
index 209751e..121ef21 100644
--- a/services/core/java/com/android/server/policy/PhoneWindowManager.java
+++ b/services/core/java/com/android/server/policy/PhoneWindowManager.java
@@ -2532,6 +2532,12 @@
                     return R.anim.dock_right_enter;
                 }
             }
+        } else if (win.getAttrs().type == TYPE_DOCK_DIVIDER) {
+            if (transit == TRANSIT_ENTER) {
+                return R.anim.fade_in;
+            } else if (transit == TRANSIT_EXIT) {
+                return R.anim.fade_out;
+            }
         }
 
         if (transit == TRANSIT_PREVIEW_DONE) {