update elements and fix some bugs

lib/paper_button_behavior.dart

Index: lib/paper_button_behavior.dart
diff --git a/lib/paper_button_behavior.dart b/lib/paper_button_behavior.dart
index 75b7b286c3483640e7faa9c2b4e0a6569bfcccc9..575e981b0ce206d64fd6c57714438da4c874eca4 100644
--- a/lib/paper_button_behavior.dart
+++ b/lib/paper_button_behavior.dart
@@ -11,8 +11,15 @@ import 'package:polymer_interop/polymer_interop.dart';
 import 'iron_button_state.dart';
 import 'iron_a11y_keys_behavior.dart';
 import 'iron_control_state.dart';
+import 'paper_ripple_behavior.dart';
 
 
 @BehaviorProxy(const ['Polymer', 'PaperButtonBehavior'])
-abstract class PaperButtonBehavior implements CustomElementProxyMixin, IronButtonState, IronControlState {
+abstract class PaperButtonBehavior implements CustomElementProxyMixin, IronButtonState, IronControlState, PaperRippleBehavior {
+
+  /// 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.
+  num get elevation => jsElement[r'elevation'];
+  set elevation(num value) { jsElement[r'elevation'] = value; }
 }