Implement MouseEvent buttons attribute.

LayoutTests/fast/events/mouse-event-buttons-attribute-expected.txt

Index: LayoutTests/fast/events/mouse-event-buttons-attribute-expected.txt
diff --git a/LayoutTests/fast/events/mouse-event-buttons-attribute-expected.txt b/LayoutTests/fast/events/mouse-event-buttons-attribute-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..13107c748ba414561b676ff495add0e19b7a91cc
--- /dev/null
+++ b/LayoutTests/fast/events/mouse-event-buttons-attribute-expected.txt
@@ -0,0 +1,49 @@
+MouseEvent::click test [leftButton,rightButton]

[Rick Byers, 2014/11/18 20:29:18]

this output looks great - thank you!

+PASS buttons is 3
+
+MouseEvent::dblclick test [leftButton,middleButton]
+PASS buttons is 5
+
+MouseEvent::mousedown test [leftButton,middleButton,rightButton]
+PASS buttons is 7
+
+MouseEvent::mouseup test [rightButton]
+PASS buttons is 2
+
+MouseEvent::mousemove test [leftButton]
+PASS buttons is 1
+
+MouseEvent::mouseenter test [rightButton,middleButton]
+PASS buttons is 6
+
+MouseEvent::mouseleave test [leftButton,rightButton]
+PASS buttons is 3
+
+MouseEvent::mouseover test [leftButton,middleButton]
+PASS buttons is 5
+
+MouseEvent::mouseout test [leftButton]
+PASS buttons is 1
+
+WheelEvent::mousewheel test [leftButton,rightButton]
+PASS buttons is 3
+
+GestureEvent::mousedown test [leftButton]
+PASS buttons is 1
+
+GestureEvent::mouseup test [leftButton]
+PASS buttons is 1
+
+GestureEvent::click test [leftButton]
+PASS buttons is 1
+
+GestureEvent::dblclick test [leftButton]
+PASS buttons is 1
+
+GestureEvent::mousemove test [leftButton]
+PASS buttons is 1
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+