Migrate docked divider drawing to SysUI

Move docked divider drawing to SysUI. This let's us have real
time shadows in the future. Keep DockedStackDividerController
for placing/visibility in window manager.

Change-Id: I82c10add626d30f2ba180ee2a21cdbe6ddfe0371
diff --git a/core/java/android/view/WindowManager.java b/core/java/android/view/WindowManager.java
index 92e473d..2d0435f 100644
--- a/core/java/android/view/WindowManager.java
+++ b/core/java/android/view/WindowManager.java
@@ -50,6 +50,18 @@
  * @see android.content.Context#WINDOW_SERVICE
  */
 public interface WindowManager extends ViewManager {
+
+    /** @hide */
+    int DOCKED_INVALID = -1;
+    /** @hide */
+    int DOCKED_LEFT = 1;
+    /** @hide */
+    int DOCKED_TOP = 2;
+    /** @hide */
+    int DOCKED_RIGHT = 3;
+    /** @hide */
+    int DOCKED_BOTTOM = 4;
+
     /**
      * Exception that is thrown when trying to add view whose
      * {@link LayoutParams} {@link LayoutParams#token}