Files.app: Add a deduplication step to avoid importing duplicate media.

ui/file_manager/file_manager/background/js/task_queue.js

Index: ui/file_manager/file_manager/background/js/task_queue.js
diff --git a/ui/file_manager/file_manager/background/js/task_queue.js b/ui/file_manager/file_manager/background/js/task_queue.js
index 43ebb70b4b0e8290b301ee14991fd1e9f29bc882..9f2d539432627cd9e7ca58dd39a8552ca4f93b7f 100644
--- a/ui/file_manager/file_manager/background/js/task_queue.js
+++ b/ui/file_manager/file_manager/background/js/task_queue.js
@@ -52,7 +52,7 @@ importer.TaskQueue.prototype.queueTask = function(task) {
   // The Tasks that are pushed onto the queue aren't required to be inherently
   // asynchronous.  This code force task execution to occur asynchronously.
   Promise.resolve().then(function() {
-    task.addObserver(this.onTaskUpdate_.bind(this));
+    task.addObserver(this.onTaskUpdate_.bind(this, task));
     this.tasks_.push(task);
     // If more than one task is queued, then the queue is already running.
     if (this.tasks_.length === 1) {
@@ -91,11 +91,11 @@ importer.TaskQueue.prototype.setIdleCallback = function(callback) {
 /**
  * Sends out notifications when a task updates.  This is meant to be called by
  * the running tasks owned by this queue.
- * @param {!importer.TaskQueue.UpdateType} updateType
  * @param {!importer.TaskQueue.Task} task
+ * @param {!importer.TaskQueue.UpdateType} updateType
  * @private
  */
-importer.TaskQueue.prototype.onTaskUpdate_ = function(updateType, task) {
+importer.TaskQueue.prototype.onTaskUpdate_ = function(task, updateType) {
   // Send a task update to clients.
   this.updateCallbacks_.forEach(function(callback) {
     callback.call(null, updateType, task);
@@ -146,7 +146,13 @@ importer.TaskQueue.prototype.runPending_ = function() {
 importer.TaskQueue.Task = function() {};
 
 /**
- * @typedef {function(!importer.TaskQueue.UpdateType, !importer.TaskQueue.Task)}
+ * A callback that is triggered whenever an update is reported on the observed
+ * task.  The first argument is a string specifying the type of the update.
+ * Standard values used by all tasks are enumerated in
+ * importer.TaskQueue.UpdateType, but child classes may add supplementary update
+ * types of their own.  The second argument is an Object containing
+ * supplementary information pertaining to the update.
+ * @typedef {function(string, Object=)}
  */
 importer.TaskQueue.Task.Observer;
 
@@ -196,13 +202,14 @@ importer.TaskQueue.BaseTask.prototype.addObserver = function(observer) {
 importer.TaskQueue.BaseTask.prototype.run = function() {};
 
 /**
- * @param {!importer.TaskQueue.UpdateType} updateType
+ * @param {string} updateType
+ * @param {Object=} opt_data
  * @protected
  */
-importer.TaskQueue.BaseTask.prototype.notify = function(updateType) {
+importer.TaskQueue.BaseTask.prototype.notify = function(updateType, opt_data) {
   this.observers_.forEach(
       /** @param {!importer.TaskQueue.Task.Observer} callback */
       function(callback) {
-        callback.call(null, updateType, this);
+        callback.call(null, updateType, opt_data);
       }.bind(this));
 };