Add Vibration API layout tests that inspect internal state.

LayoutTests/vibration/vibration-utils.js

Index: LayoutTests/vibration/vibration-utils.js
diff --git a/LayoutTests/vibration/vibration-utils.js b/LayoutTests/vibration/vibration-utils.js
new file mode 100644
index 0000000000000000000000000000000000000000..1fb0058c70d6b7eac628b23a35cb037e48295a0d
--- /dev/null
+++ b/LayoutTests/vibration/vibration-utils.js
@@ -0,0 +1,18 @@
+/**
+ * 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);
+}