[ios][eg2] Mark testRequestMobileSitePropagatesToNextNavigations as flaky.

TBR=ajuma@chromium.org

Bug: 1037663
Change-Id: I1fa106686e7cfedbbd43be0dc8b67917f74555b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1981137
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727311}

ios/chrome/browser/ui/popup_menu/request_desktop_mobile_site_egtest.mm

@@ -169,7 +169,15 @@ class UserAgentResponseProvider : public web::DataResponseProvider {
 
 // Tests that requesting mobile site of a page works and the user agent
 // propagates to the next navigations in the same tab.
-- (void)testRequestMobileSitePropagatesToNextNavigations {
+// TODO(crbug.com/1037663): Enable for EG2.
+#if defined(CHROME_EARL_GREY_2)
+#define MAYBE_testRequestMobileSitePropagatesToNextNavigations \
+  FLAKY_testRequestMobileSitePropagatesToNextNavigations
+#else
+#define MAYBE_testRequestMobileSitePropagatesToNextNavigations \
+  testRequestMobileSitePropagatesToNextNavigations
+#endif
+- (void)MAYBE_testRequestMobileSitePropagatesToNextNavigations {
   std::unique_ptr<web::DataResponseProvider> provider(
       new UserAgentResponseProvider());
   web::test::SetUpHttpServer(std::move(provider));