Add Vibration API layout tests that inspect internal state.

LayoutTests/vibration/vibration-utils.js

+/**
+ * Creates a new array with length equal to [entries]. Each entry has the
+ * value [milliseconds].
+ */
+function newPattern(milliseconds, entries) {
+  var pattern = new Array(entries);
+  for (var i = 0; i < entries; i++) {
+    pattern[i] = milliseconds;
+  }
+  return pattern;
+}
+
+/**
+ * Stop any currently running vibration. Call this to clean up internal state.
+ */
+function stopVibration() {
+  navigator.vibrate(0);
+}