Expose public API to control mIsChildViewEnabled

This is needed to replace an @UnsupportedApiUsage of the field
in appcompat/widget/DropDownListView.java

Bug: 177008210
Test: AbsListViewTest.testSelectedChildViewEnabled

Change-Id: Ia0bfe3f70f62db8185e1d9784d921e2e1f291006

core/api/current.txt

@@ -54943,6 +54943,7 @@ package android.widget {
     method protected boolean isInFilterMode();
     method public boolean isItemChecked(int);
     method public boolean isScrollingCacheEnabled();
+    method public boolean isSelectedChildViewEnabled();
     method public boolean isSmoothScrollbarEnabled();
     method public boolean isStackFromBottom();
     method public boolean isTextFilterEnabled();
@@ -54978,6 +54979,7 @@ package android.widget {
     method public void setRemoteViewsAdapter(android.content.Intent);
     method public void setScrollIndicators(android.view.View, android.view.View);
     method public void setScrollingCacheEnabled(boolean);
+    method public void setSelectedChildViewEnabled(boolean);
     method public void setSelectionFromTop(int, int);
     method public void setSelector(@DrawableRes int);
     method public void setSelector(android.graphics.drawable.Drawable);

core/java/android/widget/AbsListView.java

@@ -2656,6 +2656,27 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
         }
     }
 
+    /**
+     * Returns whether the selected child view (from the adapter's getView) is enabled.
+     *
+     * @return true if enabled
+     */
+    public boolean isSelectedChildViewEnabled() {
+        return mIsChildViewEnabled;
+    }
+
+    /**
+     * Set whether the selected child view (from the adapter's getView) is enabled.
+     *
+     * When refreshDrawableState is called, AbsListView will control the "enabled" state
+     * of the selector based on this.
+     *
+     * @param selectedChildViewEnabled true if enabled
+     */
+    public void setSelectedChildViewEnabled(boolean selectedChildViewEnabled) {
+        mIsChildViewEnabled = selectedChildViewEnabled;
+    }
+
     @Override
     protected void dispatchDraw(Canvas canvas) {
         int saveCount = 0;