Add paper-menu-button and its dependencies to third_party/polymer

third_party/polymer/v1_0/components/iron-behaviors/iron-button-state.html

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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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@@ skipping 73 matching lines @@
     observers: [
       '_detectKeyboardFocus(focused)'
     ],
 
     keyBindings: {
       'enter:keydown': '_asyncClick',
       'space:keydown': '_spaceKeyDownHandler',
       'space:keyup': '_spaceKeyUpHandler',
     },
 
+    _mouseEventRe: /^mouse/,
+
     _tapHandler: function() {
       if (this.toggles) {
        // a tap is needed to toggle the active state
         this._userActivate(!this.active);
       } else {
         this.active = false;
       }
     },
 
     _detectKeyboardFocus: function(focused) {
       this._setReceivedFocusFromKeyboard(!this.pointerDown && focused);
     },
 
     // to emulate native checkbox, (de-)activations from a user interaction fire
     // 'change' events
     _userActivate: function(active) {
       this.active = active;
       this.fire('change');
     },
 
-    _downHandler: function() {
+    _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);
     },
 
     _upHandler: function() {
       this._setPointerDown(false);
       this._setPressed(false);
     },
 
@@ skipping 52 matching lines @@
 
   };
 
   /** @polymerBehavior */
   Polymer.IronButtonState = [
     Polymer.IronA11yKeysBehavior,
     Polymer.IronButtonStateImpl
   ];
 
 </script>