Revert of Disabled flaky test AppBackgroundPageApiTest.NoJsBackgroundPage

chrome/browser/extensions/app_background_page_apitest.cc

Index: chrome/browser/extensions/app_background_page_apitest.cc
diff --git a/chrome/browser/extensions/app_background_page_apitest.cc b/chrome/browser/extensions/app_background_page_apitest.cc
index aadf45231ec078d4923a8f8a0d07a9b4a313efe2..3c134afe660375732ee963aa1835370c963b6976 100644
--- a/chrome/browser/extensions/app_background_page_apitest.cc
+++ b/chrome/browser/extensions/app_background_page_apitest.cc
@@ -304,8 +304,7 @@
   UnloadExtension(extension->id());
 }
 
-// TODO(crbug.com/642482) Disabled test for flakyness.
-IN_PROC_BROWSER_TEST_F(AppBackgroundPageApiTest, DISABLED_NoJsBackgroundPage) {
+IN_PROC_BROWSER_TEST_F(AppBackgroundPageApiTest, NoJsBackgroundPage) {
   // Keep the task manager up through this test to verify that a crash doesn't
   // happen when window.open creates a background page that switches
   // RenderViewHosts. See http://crbug.com/165138.