Add unit-tests for MenuButton and simplify implementation.

remoting/webapp/menu_button.css

Index: remoting/webapp/menu_button.css
diff --git a/remoting/webapp/menu_button.css b/remoting/webapp/menu_button.css
index d20750a9be6717c7d131038f379c648eec47b13d..e53041e7ee2f5dcfa57181f3b4e58d91470ef6f2 100644
--- a/remoting/webapp/menu_button.css
+++ b/remoting/webapp/menu_button.css
@@ -8,7 +8,7 @@
 }
 
 .menu-button-activator + ul {
-  visibility: hidden;

[Jamie, 2014/07/18 01:37:18]

visibility: hidden doesn't allow for verification using offsetWidth/Height. I
could use getComputedStyle instead; any preference?

[kelvinp, 2014/07/18 18:47:39]

I think either way is fine.  Personally, I prefer getComputedStyle and check for
the visibility or display or the element instead of checking the width and
height.

[Jamie, 2014/07/18 19:46:12]

As discussed in person, since showing or hiding the element requires a
re-layout, it would need an asynchronous browser test to do it that way, and
might be more flaky. I'm going to stick with this approach.

+  display: none;
   position: absolute;
 }
 
@@ -21,7 +21,7 @@
 }
 
 .menu-button-activator.active + ul {
-  visibility: visible;
+  display: block;
 }
 
 .menu-button-activator.active {