Bug 891213 - Defect - browser_topsites.js test does not clean up history items it adds. r=jimm

browser/metro/base/tests/mochitest/browser_topsites.js

@@ -144,7 +144,12 @@ function updatePagesAndWait() {
 
 //////////////////////////////////////////////////////////////////////////
 
+function tearDown() {
+  clearHistory();
+}
+
 function test() {
+  registerCleanupFunction(tearDown);
   runTests();
 }
 
@@ -432,5 +437,3 @@ gTests.push({
 
   }
 });
-
-