[iOS] Disable Discover Feed in Chrome Sign-in tests.

The spinner causes EarlGrey to crash following 'infinite' page wait.

Bug: 1116650
Change-Id: I20c808dfe77115ba10ba2da5ea06d60688bf76da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375173
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Auto-Submit: Nohemi Fernandez <fernandex@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801473}

ios/chrome/browser/ui/authentication/signin/BUILD.gn

@@ -106,6 +106,7 @@ source_set("eg2_tests") {
     "//base/test:test_support",
     "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui/authentication:eg_test_support+eg2",
+    "//ios/chrome/browser/ui/content_suggestions:feature_flags",
     "//ios/chrome/browser/ui/recent_tabs:recent_tabs_ui_constants",
     "//ios/chrome/test/earl_grey:eg_test_support+eg2",
     "//ios/public/provider/chrome/browser/signin:constants",

ios/chrome/browser/ui/authentication/signin/signin_coordinator_egtest.mm

@@ -9,6 +9,7 @@
 #include "base/test/scoped_feature_list.h"
 #import "ios/chrome/browser/ui/authentication/signin_earl_grey.h"
 #import "ios/chrome/browser/ui/authentication/signin_earl_grey_ui.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_feature.h"
 #import "ios/chrome/browser/ui/recent_tabs/recent_tabs_constants.h"
 #include "ios/chrome/grit/ios_strings.h"
 #import "ios/chrome/test/earl_grey/chrome_earl_grey.h"
@@ -115,6 +116,12 @@ void ChooseImportOrKeepDataSepareteDialog(id<GREYMatcher> choiceButtonMatcher) {
 
 @implementation SigninCoordinatorTestCase
 
+- (AppLaunchConfiguration)appConfigurationForTestCase {
+  AppLaunchConfiguration config;
+  config.features_disabled.push_back(kDiscoverFeedInNtp);
+  return config;
+}
+
 - (void)setUp {
   [super setUp];
   // Remove closed tab history to make sure the sign-in promo is always visible