update elements and fix some bugs

lib/src/iron-behaviors/iron-button-state.html

Index: lib/src/iron-behaviors/iron-button-state.html
diff --git a/lib/src/iron-behaviors/iron-button-state.html b/lib/src/iron-behaviors/iron-button-state.html
index 96a2bfa9f80c53444debc031634f63aa3e65980b..28cdd93fa5bbbd6d23d79b1c8942cf081c0deb00 100644
--- a/lib/src/iron-behaviors/iron-button-state.html
+++ b/lib/src/iron-behaviors/iron-button-state.html
@@ -125,33 +125,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       }
     },
 
-    _eventSourceIsPrimaryInput: function(event) {
-      event = event.detail.sourceEvent || event;
-
-      // Always true for non-mouse events....
-      if (!this._mouseEventRe.test(event.type)) {
-        return true;
-      }
-
-      // http://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/buttons
-      if ('buttons' in event) {
-        return event.buttons === 1;
-      }
-
-      // http://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/which
-      if (typeof event.which === 'number') {
-        return event.which < 2;
-      }
-
-      // http://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/button
-      return event.button < 1;
-    },
-
     _downHandler: function(event) {
-      if (!this._eventSourceIsPrimaryInput(event)) {
-        return;
-      }
-
       this._setPointerDown(true);
       this._setPressed(true);
       this._setReceivedFocusFromKeyboard(false);