Add counter metric for VirtualDevice creation

Bug: 307297730
Test: manual
Change-Id: I8112f6c2e615f512d1894f08125253414ea010f7

core/java/android/companion/virtual/flags.aconfig

@@ -49,3 +49,10 @@ flag {
   description: "Enable streaming permission dialogs to Virtual Devices"
   bug: "291737919"
 }
+
+flag {
+  name: "express_metrics"
+  namespace: "virtual_devices"
+  description: "Enable express metrics in VDM"
+  bug: "307297730"
+}

services/companion/java/com/android/server/companion/virtual/VirtualDeviceManagerService.java

@@ -65,6 +65,7 @@ import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.DumpUtils;
+import com.android.modules.expresslog.Counter;
 import com.android.server.SystemService;
 import com.android.server.companion.virtual.VirtualDeviceImpl.PendingTrampoline;
 import com.android.server.wm.ActivityInterceptorCallback;
@@ -390,6 +391,9 @@ public class VirtualDeviceManagerService extends SystemService {
                     deviceId,
                     cameraAccessController, mPendingTrampolineCallback, activityListener,
                     soundEffectListener, runningAppsChangedCallback, params);
+            if (Flags.expressMetrics()) {
+                Counter.logIncrement("virtual_devices.virtual_devices_created_count");
+            }
 
             synchronized (mVirtualDeviceManagerLock) {
                 if (mVirtualDevices.size() == 0) {