Loosen requirement that there be only one GrDrawTarget

src/gpu/GrDrawTarget.h

Index: src/gpu/GrDrawTarget.h
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index 98faffca5e8027c8ac9be6d70638f524959cf48c..db637d52b10add9e59421d726cb1bab2d44710a5 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -49,6 +49,15 @@ public:
 
     ~GrDrawTarget() override;
 
+    void makeClosed() {
+        // We only close drawTargets When MDB is enabled. When MDB is disabled there is only
+        // ever one drawTarget and all calls will be funnelled into it.
+#ifdef ENABLE_MDB
+        fClosed = true;
+#endif
+    }
+    bool isClosed() const { return fClosed; }
+
     /**
      * Empties the draw buffer of any queued up draws.
      */
@@ -235,6 +244,8 @@ private:
     bool                                        fFlushing;
     int                                         fFirstUnpreparedBatch;
 
+    bool                                        fClosed;
+
     typedef SkRefCnt INHERITED;
 };