Add Vibration API layout tests that inspect internal state.

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 32b21ad7fd18a863ebca47ead51d2e44701b18ff..d1243e7b896315585a47b8727e5aa273f2e9e077 100644
--- a/Source/modules/vibration/NavigatorVibration.h
+++ b/Source/modules/vibration/NavigatorVibration.h
@@ -54,6 +54,8 @@ public:
 
     bool isVibrating() const { return m_isVibrating; }
 
+    VibrationPattern pattern() const { return m_pattern; }
+
 private:
     explicit NavigatorVibration(Page*);
     static const char* supplementName();