Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components-chromium/paper-checkbox/paper-checkbox-extracted.js

+
+  Polymer({
+    is: 'paper-checkbox',
+
+    // The custom properties shim is currently an opt-in feature.
+    enableCustomStyleProperties: true,
+
+    hostAttributes: {
+      role: 'checkbox',
+      'aria-checked': false,
+      tabindex: 0
+    },
+
+    properties: {
+      /**
+       * Fired when the checked state changes due to user interaction.
+       *
+       * @event change
+       */
+
+      /**
+       * Fired when the checked state changes.
+       *
+       * @event iron-change
+       */
+
+      /**
+       * Gets or sets the state, `true` is checked and `false` is unchecked.
+       *
+       * @attribute checked
+       * @type boolean
+       * @default false
+       */
+      checked: {
+        type: Boolean,
+        value: false,
+        reflectToAttribute: true,
+        observer: '_checkedChanged'
+      },
+
+      /**
+       * If true, the user cannot interact with this element.
+       *
+       * @attribute disabled
+       * @type boolean
+       * @default false
+       */
+      disabled: {
+        type: Boolean
+      }
+    },
+
+    listeners: {
+      keydown: '_onKeyDown',
+      mousedown: '_onMouseDown'
+    },
+
+    ready: function() {
+      if (this.$.checkboxLabel.textContent == '') {
+        this.$.checkboxLabel.hidden = true;
+      } else {
+        this.setAttribute('aria-label', this.$.checkboxLabel.textContent);
+      }
+    },
+
+    _computeCheckboxClass: function(checked) {
+      if (checked) {
+        return 'checked';
+      }
+    },
+
+    _computeCheckmarkClass: function(checked) {
+      if (!checked) {
+        return 'hidden';
+      }
+    },
+
+    _onKeyDown: function(e) {
+      // Enter key.
+      if (e.keyCode === 13) {
+        this._onMouseDown();
+        e.preventDefault();
+      }
+    },
+
+    _onMouseDown: function() {
+      if (this.disabled) {
+        return;
+      }
+
+      var old = this.checked;
+      this.checked = !this.checked;
+
+      if (this.checked !== old) {
+        this.fire('iron-change');
+      }
+    },
+
+    _checkedChanged: function() {
+      this.setAttribute('aria-checked', this.checked ? 'true' : 'false');
+      this.fire('iron-change');
+    }
+  })