[MD Bookmarks] Restore focus after closing a dialog or context menu.

chrome/browser/resources/md_bookmarks/dialog_focus_manager.js

+// Copyright 2017 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.
+
+cr.define('bookmarks', function() {
+  /**
+   * Manages focus restoration for modal dialogs.

[tsergeant, 2017/06/28 03:47:58]

I think it's worth going into a little more detail here. Maybe add an extra
sentence like

"After the final dialog in a stack is closed, restores focus to the element
which was focused when the first dialog was opened."

[calamity, 2017/06/28 04:22:47]

Done.

+   * @constructor
+   */
+  function DialogFocusManager() {
+    /** @private {HTMLDialogElement} */
+    this.previousFocusElement_ = null;
+
+    /** @private {boolean} */
+    this.previousMouseFocus_ = false;
+
+    /** @private {Set<HTMLDialogElement>} */
+    this.dialogs_ = new Set();
+  }
+
+  DialogFocusManager.prototype = {
+    /**
+     * @param {HTMLDialogElement} dialog
+     * @param {Function=} showFn
+     */
+    showDialog: function(dialog, showFn) {
+      if (!showFn) {
+        showFn = function() {
+          dialog.showModal();
+        };
+      }
+
+      // Update the focus if there are no open dialogs or if this is the only
+      // dialog and it's getting reshown.
+      if (!this.dialogs_.size ||
+          (this.dialogs_.has(dialog) && this.dialogs_.size == 1)) {
+        this.updatePreviousFocus_();
+      }
+
+      if (!this.dialogs_.has(dialog)) {
+        dialog.addEventListener('close', this.getCloseListener_(dialog));
+        this.dialogs_.add(dialog);
+      }
+
+      showFn();
+    },
+
+    /** @private */
+    updatePreviousFocus_: function() {
+      this.previousFocusElement_ = this.getFocusedElement_();
+      this.previousMouseFocus_ = bookmarks.MouseFocusBehavior.isMouseFocused(
+          this.previousFocusElement_);
+    },
+
+    /** @private */

[tsergeant, 2017/06/28 03:47:58]

Nit: @return annotation

[calamity, 2017/06/28 04:22:47]

Done.

+    getFocusedElement_: function() {
+      var focus = document.activeElement;
+      while (focus.root && focus.root.activeElement)
+        focus = focus.root.activeElement;
+
+      return focus;
+    },
+
+    /**
+     * @param {HTMLDialogElement} dialog
+     * @private
+     */
+    getCloseListener_: function(dialog) {

[tsergeant, 2017/06/28 03:47:58]

This is nifty, I'm glad you figured out the async nastiness

[calamity, 2017/06/28 04:22:47]

Acknowledged.

+      var closeListener = function(e) {
+        // If the dialog is open, then it got reshown immediately and we
+        // shouldn't clear it until it is closed again.
+        if (dialog.open)
+          return;
+
+        assert(this.dialogs_.delete(dialog));
+        // Focus the originally focused element if there are no more dialogs.
+        if (!this.dialogs_.size) {
+          this.previousFocusElement_.focus();
+          if (this.previousMouseFocus_) {
+            bookmarks.MouseFocusBehavior.addMouseFocusClass(
+                this.previousFocusElement_);
+          }
+        }
+        dialog.removeEventListener('close', closeListener);
+      }.bind(this);
+
+      return closeListener;
+    },

[tsergeant, 2017/06/28 03:47:58]

Nit: this should be a ; not a ,

[calamity, 2017/06/28 04:22:47]

Done.

+  },
+
+  cr.addSingletonGetter(DialogFocusManager);
+
+  return {
+    DialogFocusManager: DialogFocusManager,
+  };
+});