[Linux][Flaky] Disable ChromeSignInWebViewTest.NoFindInPageForUnattachedGuest

This test has a history of flakiness (see linked bug). Although the
failure happens on Windows as well, the retry seems to succeed reliably
enough.
Flakiness Dashboard shows flakiness on linux-chromeos-rel as well, so
disabling for all of linux.

TBR=ekaramad@chromium.org

Bug: 914098
Change-Id: Idfd3680040c0dba5b52504d5808c2840611dd1c4
Reviewed-on: https://chromium-review.googlesource.com/c/1373768Reviewed-by: Friedrich Horschig [CET] <fhorschig@chromium.org>
Commit-Queue: Friedrich Horschig [CET] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615922}

chrome/browser/apps/guest_view/web_view_browsertest.cc

@@ -4280,8 +4280,15 @@ IN_PROC_BROWSER_TEST_F(ChromeSignInWebViewTest,
 // page with both an attached and an unattached <webview> and verifies that,
 // unlike the attached guest, no find requests are sent for the unattached
 // guest. For more context see https://crbug.com/897465.
+// TODO(crbug.com/914098): Address flakiness and reenable.
+#if defined(OS_LINUX)
+#define MAYBE_NoFindInPageForUnattachedGuest \
+  DISABLED_NoFindInPageForUnattachedGuest
+#else
+#define MAYBE_NoFindInPageForUnattachedGuest NoFindInPageForUnattachedGuest
+#endif
 IN_PROC_BROWSER_TEST_F(ChromeSignInWebViewTest,
-                       NoFindInPageForUnattachedGuest) {
+                       MAYBE_NoFindInPageForUnattachedGuest) {
   GURL signin_url{"chrome://chrome-signin"};
   ui_test_utils::NavigateToURL(browser(), signin_url);
   auto* embedder_web_contents =