Add fancy animation for IA fragment

The animation of IA fragment is very choppy on expanding or collapsing
conditionals. So adding LayoutTransition for IA fragment makes the
animation more smoothly.

Bug: 123536786
Bug: 123537499
Test: visual, robotests
Change-Id: I731db8556ac392c9ab98bd292498ccf6c87295fb

tests/robotests/src/com/android/settings/homepage/SettingsHomepageActivityTest.java

@@ -20,6 +20,7 @@ import static com.google.common.truth.Truth.assertThat;
 
 import android.util.FeatureFlagUtils;
 import android.view.View;
+import android.widget.FrameLayout;
 
 import com.android.settings.R;
 import com.android.settings.SettingsActivity;
@@ -65,4 +66,13 @@ public class SettingsHomepageActivityTest {
         assertThat(actualPaddingTop).isEqualTo(
                 statusBarHeight + searchBarHeight + searchBarMargin * 2);
     }
+
+    @Test
+    public void launch_shouldHaveAnimationForIaFragment() {
+        final SettingsHomepageActivity activity = Robolectric.buildActivity(
+                SettingsHomepageActivity.class).create().get();
+        final FrameLayout frameLayout = activity.findViewById(R.id.main_content);
+
+        assertThat(frameLayout.getLayoutTransition()).isNotNull();
+    }
 }