Reuse FileTasks when entries are not changed.

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

Index: ui/file_manager/file_manager/foreground/js/file_tasks.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_tasks.js b/ui/file_manager/file_manager/foreground/js/file_tasks.js
index d40eb3366139c3ff831053a90e7370620c9946e6..d4d21471d7f537a6276fb65b76f7f4583176516e 100644
--- a/ui/file_manager/file_manager/foreground/js/file_tasks.js
+++ b/ui/file_manager/file_manager/foreground/js/file_tasks.js
@@ -799,6 +799,33 @@ FileTasks.prototype.showTaskPicker = function(taskDialog, title, message,
 };
 
 /**
+ * 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.