Vibration cannot be canceled during pattern vibration.

Source/modules/vibration/NavigatorVibration.h

Index: Source/modules/vibration/NavigatorVibration.h
diff --git a/Source/modules/vibration/NavigatorVibration.h b/Source/modules/vibration/NavigatorVibration.h
index 2d3b40f58667251fca97b2be454884e3c0e516e6..06d931d03963e226cde59dc0bcc1b68bb6021ea1 100644
--- a/Source/modules/vibration/NavigatorVibration.h
+++ b/Source/modules/vibration/NavigatorVibration.h
@@ -50,6 +50,8 @@ public:
     static bool vibrate(Navigator*, const VibrationPattern&);
     static NavigatorVibration* from(Page*);
 
+    bool isVibrating() { return m_isVibrating; }
+
 private:
     explicit NavigatorVibration(Page*);
     static const char* supplementName();