Allow click events to pass through the toolbar padding.

elements/viewer-button/viewer-button.css

 /* Copyright 2013 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. */
 
 #icon {
   background-position: center center;
   background-repeat: no-repeat;
   background-size: 100% 100%;
   height: 100%;
   width: 100%;
 }
 
 :host {
   -webkit-user-select: none;
   background-image: linear-gradient(rgb(60, 80, 119), rgb(15, 24, 41));
   border: 1px solid rgb(11, 9, 16);
   cursor: default;
   display: inline-block;
   height: 36px;
   margin: 0;
+  pointer-events: all;
   width: 43px;
 }
 
 :host(:focus:host) {
   outline: none;
 }
 
 :host(:hover:host) {
   background-image: linear-gradient(rgb(73, 102, 155), rgb(32, 52, 95));
 }
 
 :host(.latchable.polymer-selected:host),
 :host(:active:host) {
   background-color: rgb(75, 103, 156);
   background-image: none;
 }