Reducing usage of magic constants in TAPL's widgets

Bug: 123904290
Change-Id: I5f158eb06ab5d40825cc975e798296ab06fc1f1f
diff --git a/tests/tapl/com/android/launcher3/tapl/Widgets.java b/tests/tapl/com/android/launcher3/tapl/Widgets.java
index 7d308af..af7d5d7 100644
--- a/tests/tapl/com/android/launcher3/tapl/Widgets.java
+++ b/tests/tapl/com/android/launcher3/tapl/Widgets.java
@@ -48,7 +48,12 @@
                 "want to fling forward in widgets")) {
             LauncherInstrumentation.log("Widgets.flingForward enter");
             final UiObject2 widgetsContainer = verifyActiveContainer();
-            mLauncher.scroll(widgetsContainer, Direction.DOWN, 1f, MARGINS, FLING_STEPS);
+            final int margin = widgetsContainer.getVisibleBounds().bottom -
+                    mLauncher.getRealDisplaySize().y +
+                    ResourceUtils.getNavbarSize(
+                            ResourceUtils.NAVBAR_BOTTOM_GESTURE_SIZE, mLauncher.getResources());
+            mLauncher.scroll(
+                    widgetsContainer, Direction.DOWN, 1f, new Rect(0, 0, 0, margin), FLING_STEPS);
             try (LauncherInstrumentation.Closable c1 = mLauncher.addContextLayer("flung forward")) {
                 verifyActiveContainer();
             }