Added more info to FLAG_ACTIVITY_LAUNCH_ADJACENT documentation

Developers need to add FLAG_ACTIVITY_MULTIPLE_TASK flag if they don't
want an existing instance of their activity to be used.

Bug: 27604971
Change-Id: I80791ba9b8a68e4ffcf7a5b9a963f27239071037
diff --git a/core/java/android/content/Intent.java b/core/java/android/content/Intent.java
index 09fa5e1..182475f 100644
--- a/core/java/android/content/Intent.java
+++ b/core/java/android/content/Intent.java
@@ -4560,7 +4560,8 @@
     /**
      * This flag is only used in split-screen multi-window mode. The new activity will be displayed
      * adjacent to the one launching it. This can only be used in conjunction with
-     * {@link #FLAG_ACTIVITY_NEW_TASK}.
+     * {@link #FLAG_ACTIVITY_NEW_TASK}. Also, setting {@link #FLAG_ACTIVITY_MULTIPLE_TASK} is
+     * required if you want a new instance of an existing activity to be created.
      */
     public static final int FLAG_ACTIVITY_LAUNCH_ADJACENT = 0x00001000;