Bug 874843 - Fix typo in test r=typo

layout/generic/test/test_plugin_clipping_transformed.xhtml

@@ -12,7 +12,7 @@
 var child;
 function childDone() {
   child.close();
-  SimpleTest.executeSoon(SimpleTest.finish());
+  SimpleTest.executeSoon(SimpleTest.finish);
 }
 
 if (navigator.platform.indexOf("Mac") == 0) {

layout/generic/test/test_plugin_focus.html

@@ -10,7 +10,7 @@
 var child;
 function childDone() {
   child.close();
-  SimpleTest.executeSoon(SimpleTest.finish());
+  SimpleTest.executeSoon(SimpleTest.finish);
 }
 
 SimpleTest.waitForExplicitFinish();