Add brief media_session cmd prompt help

Also simplify and make MediaSessionRecordImpl#mUniqueId final.

Bug: b/295518668
Test: mp droid && adb shell cmd media_session
Flag: EXEMPT refactor

Change-Id: I8ff207c8e3d104b021dcc98416ba9404db6ff7d0
diff --git a/services/core/java/com/android/server/media/MediaSession2Record.java b/services/core/java/com/android/server/media/MediaSession2Record.java
index dfb2b0a..89555a9 100644
--- a/services/core/java/com/android/server/media/MediaSession2Record.java
+++ b/services/core/java/com/android/server/media/MediaSession2Record.java
@@ -67,7 +67,6 @@
         // The lock is required to prevent `Controller2Callback` from using partially initialized
         // `MediaSession2Record.this`.
         synchronized (mLock) {
-            mUniqueId = sNextMediaSessionRecordId.getAndIncrement();
             mSessionToken = sessionToken;
             mService = service;
             mHandlerExecutor = new HandlerExecutor(new Handler(handlerLooper));
diff --git a/services/core/java/com/android/server/media/MediaSessionRecord.java b/services/core/java/com/android/server/media/MediaSessionRecord.java
index fc75bf4..0a9109b 100644
--- a/services/core/java/com/android/server/media/MediaSessionRecord.java
+++ b/services/core/java/com/android/server/media/MediaSessionRecord.java
@@ -294,7 +294,6 @@
             Looper handlerLooper,
             int policies)
             throws RemoteException {
-        mUniqueId = sNextMediaSessionRecordId.getAndIncrement();
         mOwnerPid = ownerPid;
         mOwnerUid = ownerUid;
         mUserId = userId;
diff --git a/services/core/java/com/android/server/media/MediaSessionRecordImpl.java b/services/core/java/com/android/server/media/MediaSessionRecordImpl.java
index b57b148..15f90d4 100644
--- a/services/core/java/com/android/server/media/MediaSessionRecordImpl.java
+++ b/services/core/java/com/android/server/media/MediaSessionRecordImpl.java
@@ -34,8 +34,12 @@
  */
 public abstract class MediaSessionRecordImpl {
 
-    static final AtomicInteger sNextMediaSessionRecordId = new AtomicInteger(1);
-    int mUniqueId;
+    private static final AtomicInteger sNextMediaSessionRecordId = new AtomicInteger(1);
+    private final int mUniqueId;
+
+    protected MediaSessionRecordImpl() {
+        mUniqueId = sNextMediaSessionRecordId.getAndIncrement();
+    }
 
     /**
      * Get the info for this session.
diff --git a/services/core/java/com/android/server/media/MediaShellCommand.java b/services/core/java/com/android/server/media/MediaShellCommand.java
index bea71dc..19f16cc 100644
--- a/services/core/java/com/android/server/media/MediaShellCommand.java
+++ b/services/core/java/com/android/server/media/MediaShellCommand.java
@@ -113,6 +113,7 @@
         mWriter.println("       media_session list-sessions");
         mWriter.println("       media_session monitor <tag>");
         mWriter.println("       media_session volume [options]");
+        mWriter.println("       media_session expire-temp-engaged-sessions");
         mWriter.println();
         mWriter.println("media_session dispatch: dispatch a media key to the system.");
         mWriter.println("                KEY may be: play, pause, play-pause, mute, headsethook,");
@@ -121,6 +122,9 @@
         mWriter.println("media_session monitor: monitor updates to the specified session.");
         mWriter.println("                       Use the tag from list-sessions.");
         mWriter.println("media_session volume:  " + VolumeCtrl.USAGE);
+        mWriter.println("media_session expire-temp-engaged-sessions: Expires any ongoing");
+        mWriter.println("                timers for media sessions in a temporary user-engaged");
+        mWriter.println("                state.");
         mWriter.println();
     }