update elements and fix some bugs

lib/src/paper-behaviors/paper-button-behavior.html

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 @license
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 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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 <link rel="import" href="../polymer/polymer.html">
 <link rel="import" href="../iron-behaviors/iron-button-state.html">
+<link rel="import" href="paper-ripple-behavior.html">
 
 <script>
 
   /** @polymerBehavior Polymer.PaperButtonBehavior */
   Polymer.PaperButtonBehaviorImpl = {
 
     properties: {
 
-      _elevation: {
-        type: Number
+      /**
+       * The z-depth of this element, from 0-5. Setting to 0 will remove the
+       * shadow, and each increasing number greater than 0 will be "deeper"
+       * than the last.
+       *
+       * @attribute elevation
+       * @type number
+       * @default 1
+       */
+      elevation: {
+        type: Number,
+        reflectToAttribute: true,
+        readOnly: true
       }
 
     },
 
     observers: [
-      '_calculateElevation(focused, disabled, active, pressed, receivedFocusFromKeyboard)'
+      '_calculateElevation(focused, disabled, active, pressed, receivedFocusFromKeyboard)',
+      '_computeKeyboardClass(receivedFocusFromKeyboard)'
     ],
 
     hostAttributes: {
       role: 'button',
-      tabindex: '0'
+      tabindex: '0',
+      animated: true
     },
 
     _calculateElevation: function() {
       var e = 1;
       if (this.disabled) {
         e = 0;
       } else if (this.active || this.pressed) {
         e = 4;
       } else if (this.receivedFocusFromKeyboard) {
         e = 3;
       }
-      this._elevation = e;
+      this._setElevation(e);
+    },
+
+    _computeKeyboardClass: function(receivedFocusFromKeyboard) {
+      this.classList.toggle('keyboard-focus', receivedFocusFromKeyboard);
+    },
+
+    /**
+     * In addition to `IronButtonState` behavior, when space key goes down,
+     * create a ripple down effect.
+     *
+     * @param {!KeyboardEvent} event .
+     */
+    _spaceKeyDownHandler: function(event) {
+      Polymer.IronButtonStateImpl._spaceKeyDownHandler.call(this, event);
+      if (this.hasRipple()) {
+        this._ripple.uiDownAction();
+      }
+    },
+
+    /**
+     * In addition to `IronButtonState` behavior, when space key goes up,
+     * create a ripple up effect.
+     *
+     * @param {!KeyboardEvent} event .
+     */
+    _spaceKeyUpHandler: function(event) {
+      Polymer.IronButtonStateImpl._spaceKeyUpHandler.call(this, event);
+      if (this.hasRipple()) {
+        this._ripple.uiUpAction();
+      }
     }
+
   };
 
-  /** @polymerBehavior Polymer.PaperButtonBehavior */
+  /** @polymerBehavior */
   Polymer.PaperButtonBehavior = [
     Polymer.IronButtonState,
     Polymer.IronControlState,
+    Polymer.PaperRippleBehavior,
     Polymer.PaperButtonBehaviorImpl
   ];
 
 </script>