Set a shorter timeout for logging a warn on slow IUserSwitchObservers.

On automotive, it helps identify slow services. For example:

W ActivityManager: User switch delayed: observer #1
  WallpaperManagerService sent result after 1608 ms

Without this change, the WallpaperManagerService wouldn't be logged
because the "give up" timeout is 3000ms.

Bug: 145558164
Bug: 144801993

Test: manual verification (see logcat above)

Change-Id: I68e3b7220bbac25075e4fd4dad83c3a26b88940c

services/core/java/com/android/server/am/UserController.java

@@ -130,6 +130,10 @@ class UserController implements Handler.Callback {
     // giving up on them and unfreezing the screen.
     static final int USER_SWITCH_TIMEOUT_MS = 3 * 1000;
 
+    // Amount of time we wait for observers to handle a user switch before we log a warning.
+    // Must be smaller than USER_SWITCH_TIMEOUT_MS.
+    private static final int USER_SWITCH_WARNING_TIMEOUT_MS = 500;
+
     // ActivityManager thread message constants
     static final int REPORT_USER_SWITCH_MSG = 10;
     static final int CONTINUE_USER_SWITCH_MSG = 20;
@@ -1615,9 +1619,13 @@ class UserController implements Handler.Callback {
                             synchronized (mLock) {
                                 long delay = SystemClock.elapsedRealtime() - dispatchStartedTime;
                                 if (delay > USER_SWITCH_TIMEOUT_MS) {
-                                    Slog.e(TAG, "User switch timeout: observer "  + name
+                                    Slog.e(TAG, "User switch timeout: observer " + name
                                             + " sent result after " + delay + " ms");
+                                } else if (delay > USER_SWITCH_WARNING_TIMEOUT_MS) {
+                                    Slog.w(TAG, "User switch slowed down by observer " + name
+                                            + ": result sent after " + delay + " ms");
                                 }
+
                                 curWaitingUserSwitchCallbacks.remove(name);
                                 // Continue switching if all callbacks have been notified and
                                 // user switching session is still valid