[MD History] Add UMA stats for switching views and the CBD button.

chrome/test/data/webui/md_history/test_util.js

Index: chrome/test/data/webui/md_history/test_util.js
diff --git a/chrome/test/data/webui/md_history/test_util.js b/chrome/test/data/webui/md_history/test_util.js
index 7ec8a6d7df545120647fac087afc04d05caec28f..d2ae190ecaecfc9d28468739411d5f32caf6608e 100644
--- a/chrome/test/data/webui/md_history/test_util.js
+++ b/chrome/test/data/webui/md_history/test_util.js
@@ -109,3 +109,12 @@ function waitForEvent(element, eventName, predicate) {
     element.addEventListener(eventName, listener);
   });
 }
+
+/**
+ * @return {Promise}
+ */
+function waitForAnimationFrame() {
+  return new Promise(function(resolve) {
+    requestAnimationFrame(resolve);
+  });
+}