Add defer display updates trunk stable flag

Creates defer display updates flag and
prepares unit test dependencies to
override the flag in WM tests.

Bug: 259220649
Test: atest DisplayContentTests
Test: compile and run tests locally
Change-Id: I94dcea319addd837c07825a6d85c5ea8aff6f63f

core/java/android/window/flags/windowing_frontend.aconfig

@@ -7,6 +7,14 @@ flag {
   bug: "232195501"
 }
 
+flag {
+    name: "defer_display_updates"
+    namespace: "window_manager"
+    description: "Feature flag for deferring DisplayManager updates to WindowManager if Shell transition is running"
+    bug: "259220649"
+    is_fixed_read_only: true
+}
+
 flag {
   name: "close_to_square_config_includes_status_bar"
   namespace: "windowing_frontend"

services/tests/wmtests/Android.bp

@@ -60,6 +60,7 @@ android_test {
         "truth",
         "testables",
         "hamcrest-library",
+        "flag-junit",
         "platform-compat-test-rules",
         "CtsSurfaceValidatorLib",
         "service-sdksandbox.impl",

services/tests/wmtests/src/com/android/server/wm/SystemServiceTestsBase.java

@@ -19,6 +19,7 @@ package com.android.server.wm;
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.doReturn;
 
 import android.os.Handler;
+import android.platform.test.flag.junit.SetFlagsRule;
 import android.testing.DexmakerShareClassLoaderRule;
 
 import org.junit.Rule;
@@ -27,11 +28,16 @@ import java.util.concurrent.Callable;
 
 /** The base class which provides the common rule for test classes under wm package. */
 class SystemServiceTestsBase {
-    @Rule
+    @Rule(order = 0)
     public final DexmakerShareClassLoaderRule mDexmakerShareClassLoaderRule =
             new DexmakerShareClassLoaderRule();
-    @Rule
-    public final SystemServicesTestRule mSystemServicesTestRule = new SystemServicesTestRule();
+
+    @Rule(order = 1)
+    public final SetFlagsRule mSetFlagsRule = new SetFlagsRule();
+
+    @Rule(order = 2)
+    public final SystemServicesTestRule mSystemServicesTestRule = new SystemServicesTestRule(
+            this::onBeforeSystemServicesCreated);
 
     @WindowTestRunner.MethodWrapperRule
     public final WindowManagerGlobalLockRule mLockRule =
@@ -64,6 +70,11 @@ class SystemServiceTestsBase {
         return mLockRule.waitForLocked(callable);
     }
 
+    /**
+     * Called before system services are created
+     */
+    protected void onBeforeSystemServicesCreated() {}
+
     /**
      * Make the system booted, so that {@link ActivityStack#resumeTopActivityInnerLocked} can really
      * be executed to update activity state and configuration when resuming the current top.

services/tests/wmtests/src/com/android/server/wm/SystemServicesTestRule.java

@@ -134,11 +134,20 @@ public class SystemServicesTestRule implements TestRule {
     private WindowState.PowerManagerWrapper mPowerManagerWrapper;
     private InputManagerService mImService;
     private InputChannel mInputChannel;
+    private Runnable mOnBeforeServicesCreated;
     /**
      * Spied {@link SurfaceControl.Transaction} class than can be used to verify calls.
      */
     SurfaceControl.Transaction mTransaction;
 
+    public SystemServicesTestRule(Runnable onBeforeServicesCreated) {
+        mOnBeforeServicesCreated = onBeforeServicesCreated;
+    }
+
+    public SystemServicesTestRule() {
+        this(/* onBeforeServicesCreated= */ null);
+    }
+
     @Override
     public Statement apply(Statement base, Description description) {
         return new Statement() {
@@ -168,6 +177,10 @@ public class SystemServicesTestRule implements TestRule {
     }
 
     private void setUp() {
+        if (mOnBeforeServicesCreated != null) {
+            mOnBeforeServicesCreated.run();
+        }
+
         // Use stubOnly() to reduce memory usage if it doesn't need verification.
         final MockSettings spyStubOnly = withSettings().stubOnly()
                 .defaultAnswer(CALLS_REAL_METHODS);