MD Settings: Pointers: Avoid setting mouse swap pref while mouse pressed

chrome/browser/resources/settings/device_page/pointers.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview
  * 'settings-pointers' is the settings subpage with mouse and touchpad settings.
  */
 Polymer({
   is: 'settings-pointers',
@@ skipping 14 matching lines @@
      * @const {!Array<number>}
      * @private
      */
     sensitivityValues_: {
       type: Array,
       value: [1, 2, 3, 4, 5],
       readOnly: true,
     },
   },
 
+  // Used to correctly identify when the mouse swap toggle has changed and
+  // the mouse button has been released. crbug.com/686949.
+  receivedMouseSwapButtonsUp_: false,
+  receivedMouseSwapButtonsChange_: false,
+
   /**
    * Prevents the link from activating its parent paper-radio-button.
    * @param {!Event} e
    * @private
    */
   onLearnMoreLinkActivated_: function(e) {
     settings.DevicePageBrowserProxyImpl.getInstance().handleLinkEvent(e);
   },
 
   /**
    * Mouse and touchpad sections are only subsections if they are both present.
    * @param {boolean} hasMouse
    * @param {boolean} hasTouchpad
    * @return {string}
+   * @private
    */
   getSubsectionClass_: function(hasMouse, hasTouchpad) {
     return hasMouse && hasTouchpad ? 'subsection' : '';
   },
+
+  /** @private */
+  onMouseSwapButtonsDown_: function() {
+    this.receivedMouseSwapButtonsUp_ = false;

[michaelpg, 2017/03/17 22:53:26]

Tracking two booleans is confusing, and the "why" isn't really clear.

Would only tracking mouseDown achieve the same thing? (This simplifies the
process a bit by not tracking whether the state has "changed" -- setting the
pref value to its current value should have no effect.)

onDown_() {
  this.mouseDown_ = true;
},

onUp_() {
  this.mouseDown_ = false;
  this.$.mouseSwapButton.sendPrefChange();
},

onChange_() {
  if (!this.mouseDown_)
    this.$.mouseSwapButton.sendPrefChange();
},

[michaelpg, 2017/03/17 23:09:14]

So as you said offline, keeping both booleans avoids the redundant
sendPrefChange call. If we keep them, could we rename them, e.g.
isMouseDownOnSwapToggle_ and hasSentSwapTogglePrefChange_ -- tracking the state
of things, rather than tracking which raw events we've received?

+    this.receivedMouseSwapButtonsChange_ = false;
+  },
+
+  /** @private */
+  onMouseSwapButtonsUp_: function() {
+    this.receivedMouseSwapButtonsUp_ = true;
+    this.maybeSendMouseSwapButtonsPrefChange_();
+  },
+
+  /** @private */
+  onMouseSwapButtonsChange_: function(event) {
+    this.receivedMouseSwapButtonsChange_ = true;
+    this.maybeSendMouseSwapButtonsPrefChange_();
+  },
+
+  /** @private */
+  maybeSendMouseSwapButtonsPrefChange_: function() {
+    if (this.receivedMouseSwapButtonsUp_ &&
+        this.receivedMouseSwapButtonsChange_) {
+      /** @type {!SettingsToggleButtonElement} */ (this.$.mouseSwapButton)
+          .sendPrefChange();
+    }
+  },
 });