MD WebUI: Fix incorrect positioning of action menu after window resize

ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.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.
 
 Polymer({
   is: 'cr-action-menu',
   extends: 'dialog',
 
   /**
    * List of all options in this action menu.
@@ skipping 112 matching lines @@
    * @param {!Element} anchorElement
    */
   showAt: function(anchorElement) {
     this.anchorElement_ = anchorElement;
     this.onWindowResize_ = this.onWindowResize_ || function() {
       if (this.open)
         this.close();
     }.bind(this);
     window.addEventListener('resize', this.onWindowResize_);
 
+    // Reset position to prevent previous values from affecting layout.
+    this.style.left = '';
+    this.style.right = '';
+    this.style.top = '';
+
     this.showModal();
 
     var rect = this.anchorElement_.getBoundingClientRect();

[dpapad, 2017/01/06 16:34:49]

I don't fully understand this fix. Per my own debugging at
https://bugs.chromium.org/p/chromium/issues/detail?id=667198#c2 (see video), the
getBoundingClientRect() call here returns the wrong values (clearly shown in the
video, unless I am mistaken). How is this affected by the previous values of
this.style.left/right/top? 

Are you 100% sure that this fixes the problem?

[dpapad, 2017/01/12 18:52:54]

Per explanation at
https://bugs.chromium.org/p/chromium/issues/detail?id=667198#c13, I know
understand how this fixes the issue. Thanks.

     if (getComputedStyle(this.anchorElement_).direction == 'rtl') {
       var right = window.innerWidth - rect.left - this.offsetWidth;
       this.style.right = right + 'px';
     } else {
       var left = rect.right - this.offsetWidth;
       this.style.left = left + 'px';
     }
 
     // Attempt to show the menu starting from the top of the rectangle and
     // extending downwards. If that does not fit within the window, fallback to
     // starting from the bottom and extending upwards.
     var top = rect.top + this.offsetHeight <= window.innerHeight ? rect.top :
                                                                    rect.bottom -
             this.offsetHeight - Math.max(rect.bottom - window.innerHeight, 0);
 
     this.style.top = top + 'px';
   },
 });