[Sync] Add a simple UI to sync-internals to create UserEvents.

components/sync/driver/resources/chrome_sync.js

Index: components/sync/driver/resources/chrome_sync.js
diff --git a/components/sync/driver/resources/chrome_sync.js b/components/sync/driver/resources/chrome_sync.js
index 93121fde889e76c39f8d4a0655b192a78ced7492..4d0b8d3603ad430fa21c811f6ce81c4f03b06dbb 100644
--- a/components/sync/driver/resources/chrome_sync.js
+++ b/components/sync/driver/resources/chrome_sync.js
@@ -78,6 +78,20 @@ cr.define('chrome.sync', function() {
   };
 
   /**
+   * Asks the browser if we should show the User Events tab or not.
+   */
+  var requestUserEventsVisibility = function() {
+    chrome.send('requestUserEventsVisibility');
+  };
+
+  /**
+   * Sends data to construct a user event that should be committed.

[Dan Beam, 2017/05/22 23:44:46]

can you document each @param here?

[skym, 2017/05/24 00:20:24]

Done.

+   */
+  var writeUserEvent = function(eventTimeUsec, navigationId) {
+    chrome.send('writeUserEvent', [eventTimeUsec, navigationId]);
+  };
+
+  /**
    * Counter to uniquely identify requests while they're in progress.
    * Used in the implementation of GetAllNodes.
    */
@@ -122,5 +136,7 @@ cr.define('chrome.sync', function() {
     registerForPerTypeCounters: registerForPerTypeCounters,
     requestUpdatedAboutInfo: requestUpdatedAboutInfo,
     requestListOfTypes: requestListOfTypes,
+    requestUserEventsVisibility: requestUserEventsVisibility,
+    writeUserEvent: writeUserEvent,
   };
 });