Disable flaky LaunchExternalProtocolFromSubframe.

Test is flaky on multiple platforms, not only Windows.

TBR=acolwell@chromium.org

Bug: 980446
Change-Id: I8a26aefa4beaf53c501f922e2bbc6021cd86b45e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2506578Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822159}

chrome/browser/site_isolation/chrome_site_per_process_browsertest.cc

@@ -488,18 +488,15 @@ class MailtoExternalProtocolHandlerDelegate
 // This test is not run on ChromeOS because it registers a custom handler (see
 // ProtocolHandlerRegistry::InstallDefaultsForChromeOS), and handles mailto:
 // navigations before getting to external protocol code.
-// Flaky on Windows. See https://crbug.com/980446
-#if defined(OS_CHROMEOS) || defined(OS_WIN)
-#define MAYBE_LaunchExternalProtocolFromSubframe \
-  DISABLED_LaunchExternalProtocolFromSubframe
-#else
-#define MAYBE_LaunchExternalProtocolFromSubframe \
-  LaunchExternalProtocolFromSubframe
-#endif
+
 // This test verifies that external protocol requests succeed when made from an
 // OOPIF (https://crbug.com/668289).
+
+// Disabled due to flakiness. If enabled, still skip for ChromeOS based on
+// comment above.
+// See https://crbug.com/980446
 IN_PROC_BROWSER_TEST_F(ChromeSitePerProcessTest,
-                       MAYBE_LaunchExternalProtocolFromSubframe) {
+                       DISABLED_LaunchExternalProtocolFromSubframe) {
   GURL start_url(embedded_test_server()->GetURL("a.com", "/title1.html"));
 
   ui_test_utils::NavigateToURL(browser(), start_url);