Re-enable PushMessagingBrowserTest.UnsubscribeSuccess

It was disabled due to a crash that looks similar to a bug that was
fixed, issue 854993. Try re-enabling it.

Bug: 838759
Change-Id: Ia3e21a9fdccd5239af270987e6c432612f5ae15c
TBR: peter
Reviewed-on: https://chromium-review.googlesource.com/c/1352082Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611522}

chrome/browser/push_messaging/push_messaging_browsertest.cc

@@ -1652,13 +1652,7 @@ IN_PROC_BROWSER_TEST_F(PushMessagingBrowserTest, PermissionStateSaysDenied) {
   EXPECT_EQ("permission status - denied", script_result);
 }
 
-// TODO(peter): Flaky on Win buildbots. https://crbug.com/838759
-#if defined(OS_WIN)
-#define MAYBE_UnsubscribeSuccess DISABLED_UnsubscribeSuccess
-#else
-#define MAYBE_UnsubscribeSuccess UnsubscribeSucces
-#endif
-IN_PROC_BROWSER_TEST_F(PushMessagingBrowserTest, MAYBE_UnsubscribeSuccess) {
+IN_PROC_BROWSER_TEST_F(PushMessagingBrowserTest, UnsubscribeSuccess) {
   std::string script_result;
 
   std::string token1;