Feed: allow overriding feed host for testing

- chrome://snippets-internals is updated to let testers easily override
the feed host.
- If the server sends a Bless nonce, display it in snippets-internals so it
can be used by the tester.
- If the host is overridden, enable sending credentials in the request. This
is necessary for authenticating with some test servers.
- I tested that this workflow works, but it currently requires the
 --ignore-urlfetcher-cert-requests command-line switch.

Change-Id: If8fb1a0484dfbf992f84bed93eeef548b5e8f860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888387
Reviewed-by: Gabriel Charette <[email protected]>
Reviewed-by: Dan H <[email protected]>
Reviewed-by: Carlos Knippschild <[email protected]>
Reviewed-by: Mike West <[email protected]>
Commit-Queue: Dan H <[email protected]>
Cr-Commit-Position: refs/heads/master@{#711745}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index de4ea0f..623a3bd 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -215,9 +215,7 @@
 #include "components/ntp_snippets/category_rankers/click_based_category_ranker.h"
 #include "components/ntp_tiles/popular_sites_impl.h"
 #if BUILDFLAG(ENABLE_FEED_IN_CHROME)
-#include "components/feed/core/feed_scheduler_host.h"
-#include "components/feed/core/refresh_throttler.h"
-#include "components/feed/core/user_classifier.h"
+#include "components/feed/core/pref_names.h"
 #endif  // BUILDFLAG(ENABLE_FEED_IN_CHROME)
 #else   // defined(OS_ANDROID)
 #include "chrome/browser/enterprise_reporting/prefs.h"
@@ -887,9 +885,7 @@
   RecentTabsPagePrefs::RegisterProfilePrefs(registry);
   usage_stats::UsageStatsBridge::RegisterProfilePrefs(registry);
 #if BUILDFLAG(ENABLE_FEED_IN_CHROME)
-  feed::FeedSchedulerHost::RegisterProfilePrefs(registry);
-  feed::RefreshThrottler::RegisterProfilePrefs(registry);
-  feed::UserClassifier::RegisterProfilePrefs(registry);
+  feed::RegisterProfilePrefs(registry);
 #endif  // BUILDFLAG(ENABLE_FEED_IN_CHROME)
 #else
   AppShortcutManager::RegisterProfilePrefs(registry);