Add @TestApi PopupMenu.getMenuListView

This method returns the ListView representing the menu.
It is required to test the actual contents of a PopupMenu.

Bug: 34076597
Test: android.widget.cts.ToolbarTest#testItemViewAttributes,
          android.widget.cts.PopupMenuTest#testItemViewAttributes

Change-Id: Id72a8f482048d724d4fde15b126e0d08e1d18390

api/test-current.txt

@@ -48793,6 +48793,7 @@ package android.widget {
     method public int getGravity();
     method public android.view.Menu getMenu();
     method public android.view.MenuInflater getMenuInflater();
+    method public android.widget.ListView getMenuListView();
     method public void inflate(int);
     method public void setGravity(int);
     method public void setOnDismissListener(android.widget.PopupMenu.OnDismissListener);

core/java/android/widget/PopupMenu.java

@@ -17,6 +17,7 @@
 package android.widget;
 
 import android.annotation.MenuRes;
+import android.annotation.TestApi;
 import android.content.Context;
 import android.view.Gravity;
 import android.view.Menu;
@@ -281,4 +282,19 @@ public class PopupMenu {
          */
         void onDismiss(PopupMenu menu);
     }
+
+    /**
+     * Returns the {@link ListView} representing the list of menu items in the currently showing
+     * menu.
+     *
+     * @return The view representing the list of menu items.
+     * @hide
+     */
+    @TestApi
+    public ListView getMenuListView() {
+        if (!mPopup.isShowing()) {
+            return null;
+        }
+        return mPopup.getPopup().getListView();
+    }
 }