Revert recently added check to addFooterView

b/4319206

Change-Id: Ic89b2166bdc7a878ae2983d393a1d01aaa3b7d23
diff --git a/core/java/android/widget/ListView.java b/core/java/android/widget/ListView.java
index 9d29a60..d76a956 100644
--- a/core/java/android/widget/ListView.java
+++ b/core/java/android/widget/ListView.java
@@ -337,10 +337,10 @@
      */
     public void addFooterView(View v, Object data, boolean isSelectable) {
 
-        if (mAdapter != null && ! (mAdapter instanceof HeaderViewListAdapter)) {
-            throw new IllegalStateException(
-                    "Cannot add footer view to list -- setAdapter has already been called.");
-        }
+        // NOTE: do not enforce the adapter being null here, since unlike in
+        // addHeaderView, it was never enforced here, and so existing apps are
+        // relying on being able to add a footer and then calling setAdapter to
+        // force creation of the HeaderViewListAdapter wrapper
 
         FixedViewInfo info = new FixedViewInfo();
         info.view = v;