Ensure FullScreen button has classname set on render.

When the FullScreen icon is first rendered, the button within it is not having the inactive classname set. The class name is set on toggling fullscreen on/off - just not being set on render.

test/browser/spec/ol/control/fullscreen.test.js

@@ -7,4 +7,23 @@ describe('ol.control.FullScreen', function () {
       expect(instance).to.be.an(FullScreen);
     });
   });
+
+  describe('the fullscreen button', function () {
+    describe('when inactiveClassName is not set', function () {
+      it('is created with the default inactive classname set on the button', function () {
+        const instance = new FullScreen();
+        const button = instance.button_;
+        expect(button.className).to.equal('ol-full-screen-false');
+      });
+    });
+    describe('when inactiveClassName is set', function () {
+      it('is created with the desired inactive classnames set on the button', function () {
+        const instance = new FullScreen({
+          inactiveClassName: 'foo bar',
+        });
+        const button = instance.button_;
+        expect(button.className).to.equal('foo bar');
+      });
+    });
+  });
 });