Reuse FileTasks when entries are not changed.

ui/file_manager/file_manager/foreground/js/task_controller.js

 // Copyright 2014 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.
 
 /**
  * @param {DialogType} dialogType
  * @param {!VolumeManagerWrapper} volumeManager
  * @param {!FileManagerUI} ui
  * @param {!MetadataModel} metadataModel
  * @param {!DirectoryModel} directoryModel
@@ skipping 244 matching lines @@
               });
         });
       });
 };
 
 /**
  * Handles change of selection and clears context menu.
  * @private
  */
 TaskController.prototype.onSelectionChanged_ = function() {
-  this.tasks_ = null;
   var selection = this.selectionHandler_.selection;
   // Caller of update context menu task items.
   // FileSelectionHandler.EventType.CHANGE
   if (this.dialogType_ === DialogType.FULL_PAGE &&
       (selection.directoryCount > 0 || selection.fileCount > 0)) {
     // Show disabled items for position calculation of the menu. They will be
     // overridden in this.updateFileSelectionAsync().
     this.updateContextMenuTaskItems_(
         [TaskController.createTemporaryDisabledTaskItem_()]);
   } else {
     // Update context menu.
     this.updateContextMenuTaskItems_([]);
   }
 };
 
 /**
  * Updates available tasks opened from context menu or the open button.
  * @private
  */
 TaskController.prototype.updateTasks_ = function() {
   var selection = this.selectionHandler_.selection;
   if (this.dialogType_ === DialogType.FULL_PAGE &&
       (selection.directoryCount > 0 || selection.fileCount > 0)) {
-    this.getFileTasks()
-        .then(function(tasks) {
-          tasks.display(this.ui_.taskMenuButton);
-          this.updateContextMenuTaskItems_(tasks.getTaskItems());
-        }.bind(this))
-        .catch(function(error) {
-          if (error)
-            console.error(error.stack || error);
-        });
+    var previousFileTasksInvalidatePromise = new Promise(function(resolve) {
+      if (this.tasks_) {
+        this.getFileTasks()
+            .then(function(tasks) {
+              if (!util.isSameEntries(tasks.entries_, selection.entries)) {

[fukino, 2017/04/26 03:01:22]

tasks_.entries_ is private.
Could you add a getter to FileTasks?

[tetsui2, 2017/04/26 07:11:17]

Done.

+                this.tasks_ = null;
+              }
+              resolve();
+            }.bind(this))
+            .catch(function(error) {
+              if (error)
+                console.log(error.stack || error);
+              this.tasks_ = null;
+              resolve();
+            }.bind(this));
+      } else {
+        resolve();
+      }
+    }.bind(this));
+    previousFileTasksInvalidatePromise.then(function() {
+      this.getFileTasks()
+          .then(function(tasks) {
+            tasks.display(this.ui_.taskMenuButton);
+            this.updateContextMenuTaskItems_(tasks.getTaskItems());
+          }.bind(this))
+          .catch(function(error) {
+            if (error)
+              console.error(error.stack || error);
+          });
+    }.bind(this));
   } else {
     this.ui_.taskMenuButton.hidden = true;
   }
 }
 
 /**
  * @return {!Promise<!FileTasks>}
  * @public
  */
 TaskController.prototype.getFileTasks = function() {
   if (this.tasks_)
     return this.tasks_;
 
   var selection = this.selectionHandler_.selection;
-  return selection.computeAdditional(this.metadataModel_).then(
-      function() {
-        if (this.selectionHandler_.selection !== selection)
-          return Promise.reject();
-        return FileTasks.create(
-            this.volumeManager_, this.metadataModel_, this.directoryModel_,
-            this.ui_, selection.entries, assert(selection.mimeTypes)).
-            then(function(tasks) {
-              if (this.selectionHandler_.selection !== selection)
-                return Promise.reject();
-              return tasks;
-            }.bind(this));
-      }.bind(this));
+  return this.tasks_ =
+             selection.computeAdditional(this.metadataModel_).then(function() {
+               if (this.selectionHandler_.selection !== selection)
+                 return Promise.reject();
+               return FileTasks
+                   .create(
+                       this.volumeManager_, this.metadataModel_,
+                       this.directoryModel_, this.ui_, selection.entries,
+                       assert(selection.mimeTypes))
+                   .then(function(tasks) {
+                     if (this.selectionHandler_.selection !== selection)
+                       return Promise.reject();
+                     return tasks;
+                   }.bind(this));
+             }.bind(this));
 };
 
 /**
  * Returns whether default task command can be executed or not.
  * @return {boolean} True if default task command is executable.
  */
 TaskController.prototype.canExecuteDefaultTask = function() {
   return this.canExecuteDefaultTask_;
 };
 
@@ skipping 54 matching lines @@
   this.metadataModel_.get([entry], ['contentMimeType']).then(
       function(props) {
         FileTasks.create(
             this.volumeManager_, this.metadataModel_, this.directoryModel_,
             this.ui_, [entry], [props[0].contentMimeType || null])
             .then(function(tasks) {
               tasks.executeDefault();
             });
       }.bind(this));
 };