WindowContainer: Obtain BLASTSyncTransaction from factory

So we don't mess up the tests using real objects.

Bug: 139371701
Test: Existing tests pass
Change-Id: Ib4be9997e8095d439b20624cf374f43e3d7aab47
diff --git a/services/core/java/com/android/server/wm/WindowContainer.java b/services/core/java/com/android/server/wm/WindowContainer.java
index e8897e1..ec90097 100644
--- a/services/core/java/com/android/server/wm/WindowContainer.java
+++ b/services/core/java/com/android/server/wm/WindowContainer.java
@@ -275,7 +275,7 @@
     RemoteToken mRemoteToken = null;
 
     BLASTSyncEngine mBLASTSyncEngine = new BLASTSyncEngine();
-    SurfaceControl.Transaction mBLASTSyncTransaction = new SurfaceControl.Transaction();
+    SurfaceControl.Transaction mBLASTSyncTransaction;
     boolean mUsingBLASTSyncTransaction = false;
     BLASTSyncEngine.TransactionReadyListener mWaitingListener;
     int mWaitingSyncId;
@@ -283,6 +283,7 @@
     WindowContainer(WindowManagerService wms) {
         mWmService = wms;
         mPendingTransaction = wms.mTransactionFactory.get();
+        mBLASTSyncTransaction = wms.mTransactionFactory.get();
         mSurfaceAnimator = new SurfaceAnimator(this, this::onAnimationFinished, wms);
         mSurfaceFreezer = new SurfaceFreezer(this, wms);
     }