[Extensions] Re-enable IncognitoApiTest.IncognitoYesScript

This test was disabled for being flaky on XP.  XP is dead.  The test now
passes 100 runs on Windows.

Bug: 248821
Change-Id: Icda344e6c7c26b5046cbf1d51929cd200792ca6f
Reviewed-on: https://chromium-review.googlesource.com/663607Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501523}

chrome/browser/extensions/extension_incognito_apitest.cc

@@ -53,14 +53,7 @@ IN_PROC_BROWSER_TEST_F(IncognitoApiTest, IncognitoNoScript) {
   EXPECT_TRUE(result);
 }
 
-#if defined(OS_WIN)
-// This test is very flaky on XP. http://crbug.com/248821
-#define MAYBE_IncognitoYesScript DISABLED_IncognitoYesScript
-#else
-#define MAYBE_IncognitoYesScript IncognitoYesScript
-#endif
-
-IN_PROC_BROWSER_TEST_F(IncognitoApiTest, MAYBE_IncognitoYesScript) {
+IN_PROC_BROWSER_TEST_F(IncognitoApiTest, IncognitoYesScript) {
   // Load a dummy extension. This just tests that we don't regress a
   // crash fix when multiple incognito- and non-incognito-enabled extensions
   // are mixed.