Add support for reporting history load with counts + timing + a 'multi-machine' dimension.

ui/file_manager/file_manager/common/js/test_tracker.js

Index: ui/file_manager/file_manager/common/js/test_tracker.js
diff --git a/ui/file_manager/file_manager/common/js/test_tracker.js b/ui/file_manager/file_manager/common/js/test_tracker.js
index a33afd784cba8cc2090eb1eb302e77250f609e41..2946a87a91affef3a60474892306d9676b182651 100644
--- a/ui/file_manager/file_manager/common/js/test_tracker.js
+++ b/ui/file_manager/file_manager/common/js/test_tracker.js
@@ -71,4 +71,8 @@ TestTracker.prototype.forceSessionStart = function() {};
  * @param {number=} opt_sampleRate
  * @return {!TestTracker.Timing}
  */
-TestTracker.prototype.startTiming = function() {};
+TestTracker.prototype.startTiming = function() {
+  return /** @type {!TestTracker.Timing} */ ({
+    send: function() {}
+  });
+};