Fix NPE when run the splitscreen test

ccfed74e82bde9ea, add the toast maker in StageCoordinator. NPE is
thrown when running the splitscreen test. It can't toast on a
thread that has not been called Looper.prepare(). This CL adds the
@UiThreadTest on needed tests to fix the NPE.

Bug: 256087248
Test: atest com.android.wm.shell.splitscreen
Change-Id: I9fef85c58570a9c1ca2741d1a8aa81439850cc88
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/SplitScreenControllerTests.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/SplitScreenControllerTests.java
index 55883ab..d01f3d3 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/SplitScreenControllerTests.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/SplitScreenControllerTests.java
@@ -39,6 +39,7 @@
 import android.content.Intent;
 import android.content.pm.ActivityInfo;
 
+import androidx.test.annotation.UiThreadTest;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
 
@@ -110,6 +111,7 @@
     }
 
     @Test
+    @UiThreadTest
     public void instantiateController_registerDumpCallback() {
         doReturn(mMainExecutor).when(mTaskOrganizer).getExecutor();
         when(mDisplayController.getDisplayLayout(anyInt())).thenReturn(new DisplayLayout());
@@ -118,6 +120,7 @@
     }
 
     @Test
+    @UiThreadTest
     public void instantiateController_registerCommandCallback() {
         doReturn(mMainExecutor).when(mTaskOrganizer).getExecutor();
         when(mDisplayController.getDisplayLayout(anyInt())).thenReturn(new DisplayLayout());
@@ -126,6 +129,7 @@
     }
 
     @Test
+    @UiThreadTest
     public void testControllerRegistersKeyguardChangeListener() {
         doReturn(mMainExecutor).when(mTaskOrganizer).getExecutor();
         when(mDisplayController.getDisplayLayout(anyInt())).thenReturn(new DisplayLayout());
@@ -134,6 +138,7 @@
     }
 
     @Test
+    @UiThreadTest
     public void instantiateController_addExternalInterface() {
         doReturn(mMainExecutor).when(mTaskOrganizer).getExecutor();
         when(mDisplayController.getDisplayLayout(anyInt())).thenReturn(new DisplayLayout());
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageCoordinatorTests.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageCoordinatorTests.java
index 8350870..3569860 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageCoordinatorTests.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageCoordinatorTests.java
@@ -50,6 +50,7 @@
 import android.window.WindowContainerToken;
 import android.window.WindowContainerTransaction;
 
+import androidx.test.annotation.UiThreadTest;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
 
@@ -113,6 +114,7 @@
     private StageCoordinator mStageCoordinator;
 
     @Before
+    @UiThreadTest
     public void setup() {
         MockitoAnnotations.initMocks(this);
         mStageCoordinator = spy(new StageCoordinator(mContext, DEFAULT_DISPLAY, mSyncQueue,