Reuse FileTasks when entries are not changed.

ui/file_manager/file_manager/foreground/js/file_tasks.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Represents a collection of available tasks to execute for a specific list
  * of entries.
  *
  * @param {!VolumeManagerWrapper} volumeManager
  * @param {!MetadataModel} metadataModel
@@ skipping 781 matching lines @@
   taskDialog.showDefaultTaskDialog(
       title,
       message,
       items, defaultIdx,
       function(item) {
         onSuccess(item.task);
       });
 };
 
 /**
+ * Compares if the given file entry set and the file entry set for this

[fukino, 2017/04/25 09:06:10]

You compare two entry lists as sets, but if previous entry set is a subset of
new entry set, this method returns true.
(considering the case when multiple entries have same URLs)

If we compare them as sets, we should fix this behavior.

More simply how about comparing them as lists? It should be lighter and works
most cases.
I'd like such general functions in util.js instead of a method of FileTasks, and
please use util.isSameEntry for consistency and future improvements.
(We might have more effective way than comparing URL in the future.)

[tetsui2, 2017/04/26 01:58:04]

Done.

+ *     FileTasks are same.
+ *
+ * @param {!Array<!Entry>} newEntries
+ * @return {boolean} return true if they are same.
+ */
+FileTasks.prototype.areEntriesSame =

[fukino, 2017/04/25 09:06:10]

nit: "are" is not common for boolean getters.

If 'isSameEntries' sounds weird to you, how about 'isSameEntryList',
'isSameEntrySet', 'isEveryEntrySame', etc...?

[tetsui2, 2017/04/26 01:58:04]

Done.

+    function(newEntries) {
+  // If the length of the entries is different, they are not same.
+  if (this.entries_.length !== newEntries.length) {
+    return false;
+  }
+  // Create set of new entry URLs.
+  var newEntryUrlSet = {};
+  for (var i = 0; i < newEntries.length; i++) {
+    newEntryUrlSet[newEntries[i].toURL()] = true;
+  }
+  // False if one of previous entries is not in the new set.
+  for (var i = 0; i < this.entries_.length; i++) {
+    if (!(this.entries_[i].toURL() in newEntryUrlSet)) {
+      return false;
+    }
+  }
+  return true;
+};
+
+/**
  * Gets the default task from tasks. In case there is no such task (i.e. all
  * tasks are generic file handlers), then return opt_taskToUseIfNoDefault or
  * null.
  *
  * @param {!Array<!Object>} tasks The list of tasks from where to choose the
  *     default task.
  * @param {!Object=} opt_taskToUseIfNoDefault The task to return in case there
  *     is no default task available in tasks.
  * @return {Object} opt_taskToUseIfNoDefault or null in case
  *     opt_taskToUseIfNoDefault is undefined.
  */
 FileTasks.getDefaultTask = function(tasks, opt_taskToUseIfNoDefault) {
   for (var i = 0; i < tasks.length; i++) {
     if (tasks[i].isDefault) {
       return tasks[i];
     }
   }
   // If we haven't picked a default task yet, then just pick the first one
   // which is not generic file handler.
   for (var i = 0; i < tasks.length; i++) {
     if (!tasks[i].isGenericFileHandler) {
       return tasks[i];
     }
   }
   return opt_taskToUseIfNoDefault || null;
 };