Create SystemApi for statsd ready broadcast

The statsd ready broadcast needs to be sent from statsd apex with
Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND flag that is @hide and cannot be
promoted to @SystemApi.
In R, this was worked around by getting the list of registered broadcast
receivers and sending them directed broadcasts to wake them up in
ag/10404099.
However, this is inefficient if there are multiple receivers so this
change creates a SystemApi for sending the actual broadcast with the
flag as recommended in ag/10404099 after it was submitted.

Bug: 150746848
Test: m
Test: flash
Test: ensure broadcast is received via logcat
CTS-Coverage-Bug: 184014462

Change-Id: I5103d8c6e87bdb47930cb7457731050da3d8e566

services/api/current.txt

@@ -105,6 +105,14 @@ package com.android.server.role {
 
 }
 
+package com.android.server.stats {
+
+  public final class StatsHelper {
+    method public static void sendStatsdReadyBroadcast(@NonNull android.content.Context);
+  }
+
+}
+
 package com.android.server.wifi {
 
   public class SupplicantManager {

services/api/non-updatable-current.txt

@@ -52,6 +52,14 @@ package com.android.server.role {
 
 }
 
+package com.android.server.stats {
+
+  public final class StatsHelper {
+    method public static void sendStatsdReadyBroadcast(@NonNull android.content.Context);
+  }
+
+}
+
 package com.android.server.wifi {
 
   public class SupplicantManager {

services/core/java/com/android/server/stats/StatsHelper.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.stats;
+
+import static android.app.StatsManager.ACTION_STATSD_STARTED;
+
+import android.annotation.NonNull;
+import android.annotation.SystemApi;
+import android.content.Context;
+import android.content.Intent;
+import android.os.UserHandle;
+
+/**
+ * Provides helper methods for the Statsd APEX
+ *
+ * @hide
+ **/
+@SystemApi(client = SystemApi.Client.SYSTEM_SERVER)
+public final class StatsHelper {
+    private StatsHelper() {}
+
+    /**
+     * Send statsd ready broadcast
+     *
+     **/
+    public static void sendStatsdReadyBroadcast(@NonNull final Context context) {
+        context.sendBroadcastAsUser(
+                new Intent(ACTION_STATSD_STARTED).addFlags(Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND),
+                UserHandle.SYSTEM, android.Manifest.permission.DUMP);
+    }
+}