update elements and fix some bugs

lib/paper_checkbox.dart

Index: lib/paper_checkbox.dart
diff --git a/lib/paper_checkbox.dart b/lib/paper_checkbox.dart
index 3d81da87c34f1e8e96be1eb98a67bcb38a61e4a1..1b223ff79528013ae70d0b85096fbc120a7ddf6d 100644
--- a/lib/paper_checkbox.dart
+++ b/lib/paper_checkbox.dart
@@ -8,10 +8,12 @@ import 'dart:html';
 import 'dart:js' show JsArray, JsObject;
 import 'package:web_components/web_components.dart';
 import 'package:polymer_interop/polymer_interop.dart';
+import 'paper_checked_element_behavior.dart';
 import 'paper_inky_focus_behavior.dart';
 import 'iron_button_state.dart';
 import 'iron_a11y_keys_behavior.dart';
 import 'iron_control_state.dart';
+import 'paper_ripple_behavior.dart';
 import 'iron_checked_element_behavior.dart';
 import 'iron_form_element_behavior.dart';
 import 'iron_validatable_behavior.dart';
@@ -19,6 +21,8 @@ import 'paper_ripple.dart';
 import 'default_theme.dart';
 import 'color.dart';
 
+/// Material design: [Checkbox](https://www.google.com/design/spec/components/selection-controls.html#selection-controls-checkbox)
+///
 /// `paper-checkbox` is a button that can be either checked or unchecked.  User
 /// can tap the checkbox to check or uncheck it.  Usually you use checkboxes
 /// to allow user to select multiple options from a set.  If you have a single
@@ -44,22 +48,14 @@ import 'color.dart';
 /// `--paper-checkbox-checked-ink-color` | Selected/focus ripple color when the input is checked | `--default-primary-color`
 /// `--paper-checkbox-checkmark-color` | Checkmark color | `white`
 /// `--paper-checkbox-label-color` | Label color | `--primary-text-color`
+/// `--paper-checkbox-label-spacing` | Spacing between the label and the checkbox | `8px`
 /// `--paper-checkbox-error-color` | Checkbox color when invalid | `--google-red-500`
 @CustomElementProxy('paper-checkbox')
-class PaperCheckbox extends HtmlElement with CustomElementProxyMixin, PolymerBase, IronA11yKeysBehavior, IronButtonState, IronControlState, PaperInkyFocusBehavior, IronFormElementBehavior, IronValidatableBehavior, IronCheckedElementBehavior {
+class PaperCheckbox extends HtmlElement with CustomElementProxyMixin, PolymerBase, IronA11yKeysBehavior, IronButtonState, IronControlState, PaperRippleBehavior, PaperInkyFocusBehavior, IronFormElementBehavior, IronValidatableBehavior, IronCheckedElementBehavior, PaperCheckedElementBehavior {
   PaperCheckbox.created() : super.created();
   factory PaperCheckbox() => new Element.tag('paper-checkbox');
 
   /// Fired when the checked state changes.
   String get ariaActiveAttribute => jsElement[r'ariaActiveAttribute'];
   set ariaActiveAttribute(String value) { jsElement[r'ariaActiveAttribute'] = value; }
-
-  /// Update the checkbox aria-label. This is a temporary workaround not
-  /// being able to observe changes in <content>
-  /// (see: https://github.com/Polymer/polymer/issues/1773)
-  ///
-  /// Call this if you manually change the contents of the checkbox
-  /// and want the aria-label to match the new contents.
-  updateAriaLabel() =>
-      jsElement.callMethod('updateAriaLabel', []);
 }