[DO NOT MERGE] Support trace command on Window Manager dumpsys

The option `dumpsys window trace` will be used to record Winscope
traces

Test: Run from the adb shell `dumpsys window trace`. Nothing should be
dumped.
Change-Id: Iab6c51d655e38a8761ebfb409745f9102ef6de34

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -225,7 +225,6 @@ import android.view.WindowManagerPolicyConstants.PointerEventListener;
 import android.view.inputmethod.InputMethodManagerInternal;
 
 import com.android.internal.R;
-import com.android.internal.graphics.SfVsyncFrameCallbackProvider;
 import com.android.internal.os.IResultReceiver;
 import com.android.internal.policy.IKeyguardDismissCallback;
 import com.android.internal.policy.IShortcutService;
@@ -6692,6 +6691,9 @@ public class WindowManagerService extends IWindowManager.Stub
                     mRoot.forAllWindows(w -> {pw.println(w);}, true /* traverseTopToBottom */);
                 }
                 return;
+            } else if ("trace".equals(cmd)) {
+                // do nothing
+                return;
             } else {
                 // Dumping a single name?
                 if (!dumpWindows(pw, cmd, args, opti, dumpAll)) {